The 3uz has a larger bore then a 1uz. The 98+ 1uz piston will fit in the block as the bore is the same, but the combustion chamber from the early head to the later head is different. I think the CC's go up in the later heads so just swaping out pistons will probably drop the compression, but I might have that backwards. David has all that info here on the site. He has done all that work already.
Bob