Take it to a machine shop, a competent one at that...
I replaced my P30 pistons with LS pistons, and had to have the LS pistons pressed off the LS rods and then have the LS pistons pressed onto the B16rods.
My little bro used a regular hydraulic press when I had a hydrolock problem (#1 rod) and it worked fine for 20k miles....
When I wanted the Piston work done (all 4), I was told to go to a machine shop to have it done properly. I did, and it only cost me $38 + $10 tip. Did it in one day!!
Oh and one machine shop told me they couldn't do it cause they would ruin the old piston... they were wrong!
Later