if i switch my psl's buttstock over to an ironwood designs sepeate buttstock and pistol grip, what other parts must i change to remain 922r compliant?
Easily obtainable US parts:
Muzzle device (or weld/pin/solder the imported device)
Plus the US butt and pistol grip gives you a total of 10 imported parts
, so you should be OK.
For a most excellent worksheet see: http://gunwiki.net/Gunwiki/BuildAkVerifyCompliance