hey ghost rider, i asked this question last year about the knock and when i put the motor in at first all i did was put my oil pump and pick up in but not my shaft.....then i tore it apart and put in my shaft and it still knocked.....so i'm still in the process of tearing it down, haven't tore off the rod caps yet.
Sorry, what a bummer!!

Did you get a chance to go over the engine with a mechanic's stethoscope for the location of the knock? When seeking out odd noises in a running engine they are invaluable. That is how I found mine when it was still at Toysport, and was just started.
Your saying the rings from the 5m will work too?
Yup! The only parts that won't interchange in the bottom end are the rods, crank, oil pump, front pulley and front crank seal. The pistons are the same as early 5M (no dome).
Be sure you have a competent machinist check the rod housing bores for size and roundness, and if you don't already have one, get a GOOD torque wrench for re-assembly.
Good luck,
Jamie