Putting a 4.2 into a 1964 3.8S vehicle.
The XJ6 III engine brackets do not work on a MK2 style...but there are mounting points on the block. My problem is that i only have the two engine rubber mounts as the car had the original engine sold before i picked it up.

So looking on the intrewebs there was a solution $67.00 each LH, RH...Boy am i gald i didnt buy those.

After measuring the transmission support rod centerline to engine rubber mount centerlines i came up with 27 inches CTC.
now subtract 1.5 inches for distance back from engine / transmission parting line and you get 25.5 inches from back of engine/tranny split to center of mounts (center of 1/2 inch by 3/4 slot)

ACCOUNTING FOR A 1/4 INCH OF CLEARANCE FOR THE THROTTLE LINKAGE AT BACK OF ENGINE BLOCK...We need 25.25 inches CTC, and using those mounting brackets that are available at MOSS or SK BARRET...would have put my engine roughly 3 inches too far into the radiator....but with my 25 1/4 inch design there is 1 1/8 inches clear from waterpump (XJ6 type) end of shaft to radiator.
NOW THAT IS A TIGHT FIT... i guess i will have to use an electric fan.
here is a picture i found (unsure of ownership, credit to whoever tried this before) but the photo shows the incorrect style mount, from an E-type...will not work on a 3.8S




But why didnt you just buy the correct brackets he says...?
well, they are no longer made...so i made my own..a work in progress