I am not 100% sure but this is what I have found.
Type 2 kits, lower safety blocks trigger, brl has a stamped sling swivel, recip charging handle
Type 3 kits, lower has a safety that does not block trigger it locks bolt, brl sling swivel is milled, recip charging handle
Type 4 kits, features of 3 but has a non recip charging handle
I hope to be around $750-1000 for a complete receiver and semi FCG for the RPD with build instructions