The Trinity 420 is not a stroker, it is a big bore. They put oversized sleeves in stock cyl's and use bigger pistons for a little extra cc. Check the bore size, the 420 is 69mm on the frist size and can go up to 71mm for oversizes. It uses a stock crank or a stock stroke long rod crank. As far as I know you have to get the pistons from Trinity. They had them made specially for them. There should be a number in the top of the piston, unless it is beat up too much to tell. If you can find the number on it just give that to Trinity... if not you will need to find out if it's got stock rods or long rods to get the correct pistons. Other than that just do a normal top end rebuild, as long as you don't find anything else wrong with it.