If they are on the list, they count even when welded into the receiver. However, only 2 parts of the complete receiver are on the list, the receiver shell and the trunnion. The other parts are irrelevant to 922r.
A full size build converted to closed bolt from a FA kit will use a US made striker (hammer) that counts, so there are 3, 4 if the bolt is new made instead of converted from the original.
Might want to check with ATF when you file your Form 1, at one time at least they said some SBRs didn't need to have US parts. The distinction was whether you shortened an existing gun or built a new gun from the start as an SBR. The letters were so confusing no one really knew which way was exempt.