The Wossners that I mentioned earlier have a pin height of 33mm, that is from the centre of the pin to the top outside edge of the piston. The DT1 piston had a 28mm pin height which it seems the YZ A&B share. So without a rod change or 5mm spacer you are stuck with genuine os pistons assuming your bore is cast iron. The LA sleeve catalouge list a sleeve for YZ250 1973-75 and it has them as originaly chrome bores.
If you still have a chrome bore and go for a taller piston you will have to use cast iron rings or the chrome will be destroyed.
