I have a failed vacuum advance on my 54 GMC. I got one from Carter (looks the same as one from Classic Trucks).
I have found out Chevy and GMC have different vacuum advances and the brackets are different. The one from Carter has problems with tube fittings and looks a little cheap. It has most of the bracket also. I would also have to drill one hole for the bracket but it could work. I did get a NOS vacuum part only (no bracket) from Chevys of the 40's that has the correct tube fittings.

The problem is that the original vacuum is spot welded to the housing bracket and the NOS is screwed on. Were Chevys screwed on also? The vacuum part seems identical to my GMC.
It seems the solution would be to hacksaw the vacuum part off the housing on my original one. I think there were 4 spot welds. Drilling seems harder as the spot welds seem larger than the drill holes would need to be for mounting purposes.

Anyone run into this?

Also interestingly the NOS was sealed completely in wax packaging for storage.