FWIW, the 500t made less HP than the 450 did, has a lower compression ratio. It does make more torque. My 450 engine went back together with a .75 overbore, new pistons and rings which I manged to nail off ebay pretty much as a matched set, someone was selling the cylinders and pistons fairly cheap. My original liners were shot, like almost rusted through to the aluminum so no go on that lane. Runs like a raped ape when I can manage to get it out of the garage when the weather is nice. She will be getting some vintage bates bags added pretty soon, starting to be nice again and I want to go MC camping. 8)
Cam chain tool can be had at Harbor Freight or you can modify and bicycle chain tool if you have the ingenuity. Harbor Freight tool might need the pin ground a little though, I've looked at getting one for a while and never have.
You have tested the compression with a teaspoon of oil in that cylinder right? If the pressure goes up significantly the rings may be worn or stuck. Stuck rings can be freed sometimes with a good soak of penetrating fluid, like PB blaster or a 50/50 mix of acetone and ATF or whatever witches brew people use. Soak a few days then fire the engine and get it hot, then test the compression.
Checking valve clearances is also a must, there's a fine line on these engines between right and tight, better to run them a little loose actually, .002" is recommended now days instead of that .0012-0015" which ever it is. Lets little more oil film happen on the cam which can make things last a little longer.
Cool project though, I still have another 450 to play with, have yet to decide what I'm gonna do with it.
How many miles is on it?