I wouldn't sleeve it - just that you have to get the bores redone properly, given the Al/Si block. A 928 shop will have the technology. One of my crew guys had his S2 engine go through a total rebuild, track/street car... went with a mild overbore, new pistons and rings from Diamond, had a 928 shop out west bore the block (can't remember the name, will ask).

Biggest PITA in that thing was timing the cams. Ended up busting the teeth off one, as well as bending valves, due to the first (failed) attempt.

Anyway, he gave a stock piston to Diamond to pattern; much less expensive that JE, I'd recommend calling them. A spare set of rings with your order is a nice bonus! Standard with them, because they normally do V8 stuff. They should also be able to do the math, I think, to adjust the pistons for bore etc as needed.

So, who are you having build it, anyway? If anything, I'd suggest a 928 builder. If not - well, the engine's just too special to trust anywhere else IMO.