Hi Jeff,
A lot to think about. I am exploring parts to rebuild the original motor, I hear TR2 or TR3 piston/liner sets will work but have not been able to compare them yet. I can not find working drawings for the various piston/liner sets used in TR's. The 3.8 was also a wet liner engine I think. They purchased the engine shop from Triumph I believe.
I know the Jag is heavy but one thought was to use the entire jag rolling chassis, motor, trans rear and suspension and only use my body. The wheelbases are close and the Jag was designed for quiet a bit more weight. I do not know the Jag that well and if I am correct, the 66 S Type did not have a full frame but only front and rear suspensions attached to the body. I could be wrong. I do admire the 3.8L engine and am still passively working o get it. It may be junk, but may also be gold.
A great holiday to everyone,
Dave