So if anyone’s interested, I ended up sending the package to The Civilian Supply in NH (right before learning an uncle I see once a year recently moved to Pawtucket lol).
Took the drive up, paid the $10/package fee for his services, checked out a few nice guns (man I’d love to have the money/reason for a cz 457 varmint) and took my XM16E1 upper home.
It was a pain to get the payment to go through at PSA. They seemed like they were rejecting my real credit card because of my MA address, but they also rejected the privacy card a couple times even when I used a random NH address. I can’t really remember what the problem might have been there, but I did eventually get it to go through with the privacy card by using a random NH address, a burner protonmail email, and I forget if I used my real phone number but I think I did.
Huge pain, yes, but despite what people here have said, there is not a cheaper way to get a gray, 1:12, chrome bcg, XM16E1 upper. Not without doing a SUBSTANTIAL amount more work, and even then you’d barely get cheaper.