You need to be careful with this, and indeed be a little cautious about some undoubtedly well meaning advice.
The link Bernard has provided to the XK140 Spare Parts Catalogue, is unfortunately to the first edition of the XK140 SPC issued in March 1955, which does not include any of the updates/changes made to the XK140 up to the last built in January 1957. Anyone with an XK140 wanting accurate information should be seeking out the second/final edition of the XK140 SPC published in February 1957.
In many cases, the March 1955 issue is good enough, but in this case, regarding your question about Inlet Manifold Studs, its not, as there was a significant upgrade/modification made to all of the Inlet Manifold Studs to eliminate a problem of a risk of the studs bottoming out, and breaking through into the Water Jacket, and thus risk of cylinder head failure.
Now as noted by Bernard, his photos are of a reproduction set of XK120 Cylinder Head studs, which do have some differences to the earlier set of XK140 studs, but should not be used in lieu of the modified/upgraded XK140 studs. I don’t know if XKs Unlimited offer the correct modified/later XK140 studs or not.
With XK140 Inlet Manifold Studs there are FIVE different part numbers, indicating being of five different lengths. Clearly the pictured set of XK120 reproduction studs show only having four lengths, and indeed without checking part numbers, cannot say how many of these XK120 studs are same as XK140 studs but given the totally different inlet manifold introduced on XK140, its unlikely that many will be the same. Which introduces another subject - how accurate do you want to be?
One of my pet hates looking at restored XK120/140/150 engines is restorers not caring about use of correct studs and their fit. Generally a factory original engine, has all its studs so specified that after protruding through various thickness of the inlet manifold, and also any clips, gaskets, carburetter-mounts etc, with an added washer, and the nut tightened in place, you get the same 1 to 1-1/2 thread protrusion visible - so it all looks neat and tidy. Many restored engines have either excessive stud protrusion, or indeed none or negative protrusion, so it all look somewhat amateurish, even if it should still be functionally and security OK.
The five different part numbers/lengths of XK140 Inlet Manifold studs are made to 1/8" length tolerance, to ensure accurate OAL for exact position on Inlet Manifold, and indeed you have to be equally careful in mounting all studs into the inlet manifold as if screwed in too tight or too loose can also vary the net protruding distance.
All inlet Manifold Studs comprise three segments. ON one end, there is a length of stud with a 5/16"UNC thread cut on, and this coarse thread is the end that screws/secures into the cylinder head casting. With XK120 studs and early XK140 studs this UNC thread is nominally 3/4" long - so can be screwed deeply into the threaded hole in the cylinder head and indeed could at times bottom out, and in certain cases break through into water jacket. Later XK140 Inlet Manifold studs have a reduced length UNC thread, to be compatible with a modified cylinder head casting that reinforces the aluminium at bottom of these UNC threaded holes. So you can use later (short UNC) studs in early XK140 and all XK120 heads, but you cannot use earlier (long UNC) XK120 and early XK140 studs in a later XK140 or XK150 head. In production, Jaguar staggered the change over point of long UNC/short UNC studs relative to the changeover of early/late XK140 ‘standard’ head and also early/late C-type head. The February 1957 Edition of the XK140 SPC gives all the relevant Part Number changes and also exact Engine Number changes for studs and cylinder head castings.
The First Edition March 1955 XK140 SPC does not provide this critical information.
If you send me your email address, I will forward to you a .pdf of the relevant section from the Feb 1957 edition of the XK140 SPC. I have a couple of original second edition books (which I personally FAR prefer to use than electronic versions, however a few yeras ago I scanned the whole second-edition into pdf format to help JCNA reproduce this later Feb 1957 SPC for their book shoppe).
But that still doesn’t give you all the different lengths of the five different Inlet Manifold Studs - as per your original question. I will send that info to you by email.