I did a little research, the '87 Lt250r wrist pin bearing is 18x23x24mm and it's too wide to fit into the ATC Honda piston with the thrust washers. I cant just use a Honda wrist pin bearing because it measures 18x22x23mm so even though it's shorter, it's too small to fit Lt250 rod.

Like I posted earlier, was planning on just taking piston to machine shop to mill it out a little but that would make it more complicated to freshen up with new piston in future if need be. So I think I found an easy alternative. A wrist pin bearing For a 77-99 RM250 measures 18x23x22mm so it's correct size for rod and it's 2mm shorter so it should allow enough room for the 2 thrust washers and proper tolerance.

My local Atv shop had one in stock so I picked it up but haven't had time to install it yet. I hope it works and I'll keep you updated.