Depends on block bore size and piston sizing. In general if they are OEM or used pistons they are best retired and replaced by purpose built / manufactured aftermarket pistons. Chances are better than good the ring lands are both worn and sized for an OEM ring and not necessarily a good choice for an aftermarket performance ring. Additionally the skirts have likely experienced varying degrees of collapse.
About five years ago I worked a deal with Gibtec Pistons for ModFords guys that would produce a set of pistons with tool steel pins, Total Seal Rings, your choice of pin locks and any compression ratio you wanted for either 2, 3, or 4 valve engines. The whole shebang was priced just under $1,200 at the time. Today I think they are between $1,200 and $1,300. The deal is still good today. The pistons are custom billet pistons built in Solidworks and manufactured on multi-axis CNC equipment by Gibtec in Denver. They are likely the finest pistons you can buy for a Modmotor today. Check out this article from the website's articles section Custom Billet Off the Shelf Pistons <= clickable.
Thank you for the info..I believe ill save up for some and as luck would have it i just got another complete gt engine for free..Though i did have a 2 hr drive one way to get it ..They kept saying it was a 02 motor but it had 21 # injectors the same as my 03..I thought that only 03 and 04 had the 21# and 99-02 had 19#..Anyhow i think i can make this one work while i save to build my project motor up..Thank you again for the info and sorry it took so long for response