I was going through my old tips No.1 book from the MGNOC and on page 40, it goes into detail on how to install pistons from a 1600cc VW motor. He used a sleeve with a 3.375 bore, a 3/32" wall and 8 1/8" long. Then he bored it to take the VW piston. He did not say if he did this on a 750 or 850 but this increased his displacement to 900.36094