After drilling out 7 rivets, 4 for the case, 3 connecting the three voltage regulators to the case, that I'd give it a test and see how the capacitors are holding up.
It actually looks to be in great condition internally, so I'll test the caps and replace them if needed, then tap out the holes left by the rivets and fit bolts instead.
For those who are interested (if anyone
Edit: And the good news is the caps all checked out just fine. I've now put it all back together. Tapped the case screws out to M4 and fitted nuts and screws to the three voltage regulators.
All back together and now running fine once again.

