The vacuum advance for "window type" Studebaker Delcos will physically interchange with most 1950s-1970s GM vehicles. For that vast range of application, there were originally at least 25 different part numbers, with important differences in the operational specs; primarily, vacuum required for full advance, and total degrees of advance. However, vacuum advance technology ceased in the 1970s and has became almost forgotten technology. So now days, VAs have became a one size fits all, as long as it physically fits. The one size fits all for GM vehicles is Echlin #VC680, which is readily available at FLAPS for $10-15, and is also referenced on this NG as a replacement for Studes. It is also the same one I removed from a Stude distributor a couple days ago.
The problem is, the Stude VA is supposed to advance 16 degrees at 12 inches' vacuum, but the VC680 only advances 12 degrees, and requires 16-18 inches' vacuum to do so. So that vac advance will almost certainly result in lost pep and MPG in a Stude. In researching VA specs on-line, the closest to Stude I found was VC1812, which advances 12 degrees at 12-14 inches' vacuum. With that VA on a Stude, the 2 degrees' less advance could be offset by advancing the timing a couple of degrees.
I found a better answer at Summit, with an adjustable VA, made by Accel. A couple of other companies also make the adjustables. Will report more when I receive it.
Bottom line, for anyone running a window type Delco in a Stude, if you are not satisfied with MPG or pep, the VA is a good place to look when it comes to troubleshooting.