First of all, my commiserations.

My 83 was rear ended twice. Definitely get a good body shop to look at it. I had a place that did concourse restorations fix mine.

PnP's can be good for parts but 83 - 85 can be a bit specific, i.e. bumper trim, bumper shocks, etc. so it's wherever you can get the part basically; e-bay if necessary. I guess it depends how fast you want to get it done.

It's a true downer having your unblemished Old Faithful take an undeserved shot, but you are handling it in the right spirit.

You're on the right track taking it to a body shop for an evaluation...see if you can get a trusted 'car person' to recommend one, or ask the Volvo dealer who they use.

When I got tapped in the rear of our 83 it didn't look like much but it was a $1600 repair! This was in 1998. The unibody had been tweaked slightly and needed straightening (lifted the carpet in the trunk, and there was the cracked/crazed paint on the 'frame'), the bumper shocks had been compressed beyond their limit so had to be replaced, a broken taillight, a slight dent, a new bumper cover, and some repainting. His insurance paid.

I'm not suggesting you will want to hit the at-faults up for that kind of money, but once you get a professional opinion of the exact damage and costs for full repair, you can decide what your options are.

And the guilty party might be much happier to 100% fund your DIY proposal when they see the pro's estimate.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and a few old motorcycles)