As has been said before the A series engine with no noticeable internal differences but maybe a diffrent carburetor/induction would work best with say a 1 3/4" straight thru exhaust, if the engine has had say head work, differnt cam, pistons, crank work and a quite larger carby say 40mm or duals then 2 to 2.5" would work better....

Extractors are always a great way to get the A series alive and kicking, some 4-2-1 (tunned length would be better) extractors would be better suited than say the 4-1's but both a great upgrade!

Yeah the B310 standard pipe is a little pee shooter, i think its 1" to 1 1/4" pipe, its crap!

anders8b id be opting for a 1 3/4" strait thru exhaust if i were you, depending if future upgrade is on the cards or not..

Dave