I agree with tsillay, A12's can be bored to 76mm easily (mine's 78mm, but its a A12A).

There is a pin to top of piston issue, but don't thinks its a biggie and from memory decking the block fixes it.

As to other enhancements, well depends on how many ponies you want and what you want to do with it when complete. If you talking a good road engine, then 10.5:1 compression, a little head porting, bigger valves, side drafts, extractors/headers and a mild to medium cam ....