The shaved lugs would really burn me. Contact the person who sold the AK-74 kit to you and make sure they make it right. Have them pay for a replacement gas block... a replacement front sight block too, if that was shaved. Or have them pay to have the FSB and gas block re-welded.
Yes, you can still rivet it, it will not work loose.
On the VECTOR... Is that made with a US barrel, or is it a kit built in the US? I really doubt Vector welded it, that is an awful lot of trouble to go through when pinning is so much easier, especially when if it was an original kit, the FSB would already be pinned in place with no reason to remove it.