Next time you do this, Put 4 bolts in the flange and make 2 loops with some bailing wire so that you can hook the loops with the strap so that force is centered on the stub axle (no tapping with mallet needed), leaving the center unobstructed to install the c-clip.
I have a tool I made from 1/4" plate. It's basically the same as the dealer tool, only less fancy since I made it in about 20 minutes. Works great. I've never tried installing a flange without it, and I don't think I would want to. Oh, and those aren't overheat marks on the CV cups; they're heating marks from sections that were surface hardened. Most CV joints you look at will have those marks.
A good way to keep those broken thrust washers in is to use some small dots of grease on them and that will hold them to the shaft a little better. The grease will just wash into the trans fluid and do no harm. I've used small amounts of grease to hold small or difficult parts in their place before securing them and it works 90% of the time.
On my gasser 1992 golf gl there is indeed a heat sheild over the axle. On my 87 golf diesel however, there was no heatsheild and there were no issues.
ok, this car is now for sale along with a mountain of parts for 1500 bucks in the for sale section if you are interested. Trying to put together savings to get married, I should have eloped when I had the chance, but the GF got excited about an actual wedding, and here we are. If you have any interest in this car, please PM me. After the wedding and bills are paid, ill buy another one