Many engine come with extra shims, not installed in the engine
the need to add shims depends on many things
Most cases you don't need them. but if you're running high nitro% sometimes you will need to add a shim.

Massivsmods,
You sure you have the right connecting rod for that motor??
Are you sure it's a P5? the cases all look much the same
you maybe putting a P5 P/S into a BS21SB which is a short stroke motor
Or the guy you got it from sold you a "Frankin Motor"

Just a guess
Good luck