After doing more work on my seatbelts I think I've changed my mind on the attachment of the retractor reinforcement plates. I don't want to plug weld the plates in so I made two more 1/8" steel plates that go on the retractor side of the sheetmetal the same size as the anchor plate. I'm going to use five or six 1/4" grade 8 flathead screws through both plates, sandwiching the sheetmetal between them. I think the screws will be stronger than plug welds anyhow, and I won't have to worry about making a good plug weld through a 1/8" plate onto the sheetmetal. The 7/16" bolts will also go through both plates and the sheetmetal.