The big issue with the classic Jag six is weight- the outer (really non-load-bearing) walls are 3/4"+ thick in many places because of the antique pttern making and foundry-eork inside and the smooth, filled in walls on the outside. I've heard over 800lbs for a long block. I do know for sure that if you convern a Jag sedan to SBC or Ford Cleland power (either being in all iron) you have to cut the front springs, not for looks or hanlding , but so the car doesn't look like it's mising its engine.
To me it's neither fish nor fowl- not modern, and not really classically simple and durable like a 248/270 or a Packard or Buick inline.
