In my quest for the "perfect" sleeper Jag sedan, I bumped the compression up to 10-1, installed 

a 3 carb set up (three S.U. HD8's) that is supposed good for an automatic bolt on 50 H.P.

I also installed a series 3 cylinder head upsizing the valve size from 1.5 inches to 1.875 inches. This modification is known to bring about 20 HP 

to the game.

Included in the head up grade were (are) a full set of tulip shaped valves from Rob Beere Racing out of England.