G'day mate, my concern with using the oil pump would be whether the engine would get enough oil.
Did you get your kit from autotech355? If so, the piston should be ok, I ran mine with no problem, it was the 47mm piston that I had to trim the skirts, this was a cheap chinese kit, having said that, it goes pretty well.
To trim the skirts, I just cut the corners off with a hacksaw and then filed the edges smooth, I don't have a pic of the trim, but I will try to include a pic of the piston, but lately i can't seem to upload pics.
In my thread ZX50 Build,,,Again!!! there is a pic titled clearance check 2, if you have a look at that one you can see where the skirt would hit the crank weight, the corner you see is what I cut off, I didn't get at all technical with it, just measured up 10mm and along the bottom 10mm drew a line and cut, did the same on all four corners.