I’m a bit confused regarding 1960s 4.2 engines , there’s a lot of expertise on here ,so hopefully some clarity !
I know that early ones had short head studs ,like 3.8 etc.& their cylinder heads were slightly shorter than later .
What engine numbers did the longer studs come in ? & are there visible external features on an engine that will tell you ?
Did the 2 extra rear water holes come in later than the long studs or same time ?
I have seen a May 1967 420 sedan engine ( 7F 78** ) which has the slight extension on the rear of the head & has a large plate with 7 screws on the rear of the block.
I have seen a straight port head which has the extension at the rear , but no extra water holes. Possibly from a 240 or 340 ? Guess all 240/340 had this ?
I have seen the following engine numbers as being when the extra water holes came in , not sure how accurate.
420G 7D 58882
420 7F 11173
E type 7R 1915
E type 7R 35389
XJ6 7L 1176
Presumably at any one time , the 4.2 blocks in all the models , 420G,420, E type , Xj6 were the same ?
Interested to get some feedback , thanks in advance !