I'm a bit worried about this wear on the surface of the control arm mount. The bolt hole is elongated slightly as well.

If it needs a repair, what is the correct way to go about it?

Also, there was a gasket between the steering knuckle and the backing plate, any thoughts on how to acquire a replacement? (66 Delta 88)

 

Weld the wear marks in and then grind them flat. New bushings will keep things from wearing again. Stay on top of the bushing replacement and you shouldn't ever need to worry about it again.

Rob did it in this thread. Great reading and points out the pitfalls and MAWs.

https://classicoldsmobile.com/forums...t-end-job.html

 

That "gasket" is just a spacer to help alignment and noise deadener for squeaks for the backing plate. The simplest answer will be getting a sheet of similar material from Autozone or similar (they all sell packs of "make your own" gasket sheets) and cut out a roughly similar circle.

Right Stuff Detailing and similar folks include them with the spindle + backing plate kits. I'm not seeing it available separately on quick glance, but they may be willing to sell you some if you call them up. I am making the assumption that the dimensions there are the same between B body and A body.

It's not a precision piece, so quick and simple may be the way.

Agreed with cjsdad on the lower. Make sure it's strong and clean up the surface. Weld up if it needs it. The alignment can fix any minor relocation of the ball joint due to that small amount of wear. If it doesn't clean up well then it may be worthwhile using large hardened washers between the bolt and the mount, if the bolt head and nut are chewing into the mount.
The main clamping that I'm aware of actually occurs on the inside of the mount, between the center support tube and the rubber bushing against the inside of the mount, with the bolt providing the clamping force to keep them together. So a precise hole for the bolt is good, but the bolt shouldn't be rotating or attempting to move anyway.

 

One of the aftermarket outfits (forget which at the moment) sells those "seals" for between the knuckle and the backing plate. I think I paid $4.00 for a pair of them about two years ago.

 

on my stockcar,we used large washers,put a steel rod,(same size as the bolts) through the holes of both mounts to keep the washers aligned, and weld the washers to the frame. thickness of washers should be somewhere near frame thickness