Nick,
The subject of C-type heads is most complex, with much confusion and misunderstandings, and indeed as noted earlier, most current books on XK120 Originality have simply got it totally WRONG.
Accordingly, I maintain a simple position that no new XK120 sold to a private customer, was ever fitted with a factory original C-type head.
As I said a simple position that covers 99.97% of all XK120s made, based on current proof/research and the fact there were some 12000 XK120s made.
The first complication is what exactly is a C-type head?
The very first ‘works’ C-types that raced at LeMans in 1951 had probably a standard XK120 A-type head to Special Equipment specification (Cams and valves), and was probably ‘blue-printed’, and was fitted with a standard XK120 Inlet Manifold and twin H6 (1-3/4in) carburetters, but manual choke versions, and not the Thermo-choke H6 carburetters as fitted to XK120/Mark VII.
After 1951 LeMans, a decision was made to ‘develop’ the C-type based on feedback of 1951 performance/competiveness etc, including the engine. The ‘Works’ C-types prepared for 1952 LeMans were significantly upgraded, including developing the cylinder-head, inlet manifold and carburetters. The cylinder head casting remained the standard XK120 A-type casting, but was hand modified to improve its power/torque potential, along with the newly developed 2inch H8 carburetters.
This June 1952 Engine, retrospectively had what I now refer to loosely as the first version C-type head, albeit Jaguar didn’t call it that - but lets now say this race/experimental head was the first C-type head, version C1.
Jaguar then decided that they wanted to compete in European Production Sports Car races, which required reasonable proof of putting the XK120C into ‘production’ and accordingly developed/built a batch of 50 ‘Production’ C-types. The cylinder head for these cars was a total new casting - Jaguar Part Number C.7700, that after machining and a certain amount of hand fettling was assembled up to be a C.7707 cylinder head (basic assembly - no valves/cams etc yet fitted). These heads as prepared especially for the ‘production’ C-type, were now identified by Jaguar as being the second (main) variant head, and were identified as C2. (Now I dont know, but I suspect C2 means second Competition head, not second C-type head, but it really doesn’t matter, lets just call them C2 heads).
Now these C2 heads are most probably what was offered via Service Bulletin 95B, as being available for XK120 owners wanting to upgrade their used XK120s (that had originally been delivered new/fitted with a normal XK120 A-type head) The reality is at most, a handful of C2 heads were actually sold/delivered, and then only to special or sponsored customers (by sponsored I mean on the strong recommendation of the Jaguar Distributor in the country where XK120 was being raced.
So there were at least 50 C2 heads made for all the production C-types, a ‘handful’ only sold to be fitted/upgraded used racing XK120s, plus works spares, plus ‘production’ C-type spares, and maybe a few more for special purposes/applications on other than C-types or racing XK120s. How many all up, no idea, and no one (I am aware of) has ever found any factory records advising quantity and disposition of C2 heads. At a guess, more that 50 total (definately), but less than 100 total (probably less than 75).
Now things went two directions now, the C2 head (C7700 casting) was further developed into the so called D-type head (as first seen in June 1954 LeMans), but there was also a decision to make a series production C-type head to be offered as a readily available optional extra on the new model XK140 as released/on sale from October 1954. This new ‘series production’ C-type head was now a revised casting C.7707, but on basic maching/assembly remained a C.7707 part number head assembly (again not counting all the later bolt-ons, like studs, camshafts, valves etc). These ‘third’ variant heads were now identified by factory as C3 heads, and indeed are readily identified/confirmed by having on the under-surface the cast in lettering C7707 and C3.
Now these C3 series-production heads as available from the introduction of the XK140 model only, were very much marketed as having C-type heads, but initially could only be readily identified by the new XK140 customer by being painted red, and indeed by having in a stamped in Engine Number with a -8S or -9S (or -7S) suffix. These 1954 and early 1955 made C3 heads did NOT have the large cast in letter ‘C’ in the spark plug valley. Now I speculate this caused a ‘marketing/customer satisfaction dilemma’ as all an XK120SE owner with his A-type head, with an Engine Number stamped -8S or -9S, had to do, was paint it red to impress his mates. So Jaguar decided from early 1955 to now also add a large cast ‘C’ in the spark plug valley, but with no other changes, these still C3 heads remained with C7707 and C3 cast on the underside. . Later in mid 1956, another minor change to the casting/associated machining prompted a part number upgrade to now be C7707/1, but underneath was now a cast C7707-1 and still C3 .
C7707 C3 heads became readily available either as a new spare part from Oct 1954 onwards, or indeed as a wrecked XK140MC used spare part.
So the question - were any XK120s ever fitted from new with a C-type head, the answer is a simple NO, if you are referring to the readily understood/identified/available third variant C7707 C3 C-type head.
But if you know exactly what you are looking for, there has been a small handful only C7700 C2 cylinder heads now found/confirmed not originally fitted to a ‘production’ C-type, so a spare-part head as per that offered under SB95B (to very special customers) and indeed three only that can confidently be determined as being fitted from new by the factory to a new (very special) customer XK120.
Thus stated SIMPLY in one sentence/breath - there were NO XK120s fitted with a C-type head from new as original equipment.
Yes, its possible that that number three may indeed increase, as indeed the number of C2 ‘Competition’ Heads supplied under SB95B to used/racing XK120s (and maybe other cars - Cooper Jaguar, Lister Jaguar and similar) may also increase from the current ‘small handful’, but keep in mind the very small window of opportunity - from mid/late 1952 up until 1954.
AS you can appreciate - there is a LOT more to all of this, and indeed ‘one day’ may well be written up/published with photos if/when it becomes a priority. Those really interested, I do talk to direct and compare notes/research/possible sightings.
