Big Block Ford Mahle 557 Forged Piston & Ring Set, brand new in box supplied by SummitRacing, for use with 4.5" stroke crank and 6.7" rods, or 4.3" stroke with 6.8" rods, 38cc dish, 4.44" bore (+0.080). Pistons don't get much better or stronger than this. Full description is here: http://www.summitracing.com/int/parts/mle-bbf350440i38.
Compression with 74cc heads is 10.3:1, with 95cc heads is 9:1. Viewing welcome in Nottingham, can courier for a tenner, £390.