I visited the most likely looking welding shop in the area to see if they could repair the margin rack latch part. They felt it was not possible due to the very small size of the broken off part. Will keep looking at my plans B, C and D.
PERTEC D3422 DRIVE RESTORATION
I found that the 25V raw power fuse had blown, a 10A 3AG type, which I picked up and installed in order to diagnose the state of the drive. I discovered that one of the motor plugs was not replaced when I reinstalled the power supply assembly. Perhaps this was the cause of the chain of events leading to a puff of smoke and the fuse blowing.
Installing a new fuse, I again saw smoke but once again couldn't localize it to the exact component(s) before it stopped. The fuses are popping too quickly to spot the smoke source, so I began a more rigorous checkout through the circuit.
Unhooking the logic board doesn't stop the fuse blowing behavior. Since I saw the smoke on the servo board (which also houses the power supply regulators), there is probably something bad on the board. However, it could have been due to a problem in some attached circuit, such as a short circuit that overloaded the parts on the servo board.
If I could see any obviously damaged parts, it would be easier, but everything is seemingly as good as new. I will try to isolate all the circuits that plug into this board, checking them for reasonableness, hoping to locate a primary cause for the smoke.