MRC Variac+ -- NEED HELP identifying this antique electronic
Probably a low voltage/high current AC source.
The Variac is relatively low VA compared to the range of the CT/ammeter, and there appears to be a transformer or inductor with a high-current winding in addition to the metering current transformer.
It could be a source for measuring material characteristics of highly conductive samples, or a source for resistance welding, but the company name would tend to imply the former.
Measure the voltage at the terminal block vs. Variac setting. You might also want to determine if the output is isolated from the mains.
Edit: Based on the Wikipedia page, I'm going to make a wild guess that this is a high current source used for vacuum evaporation. The 'boat' used in the vacuum chamber would look something like this:

The aluminum part at the bottom with the copper rods going through it is a high-current vacuum feedthrough. Looks like the conductors are liquid cooled via internal channels.