Are you using the scratchplate to bridgeplate measurement as a way of locating the bridge? If you are, you're much better of getting a nut to bridgeplate measurement or setting the saddles in the middle of their adjustment range and measuring out the scale length from the nut to the saddles.
That's a nice project. I just replaced the pots in buddy's Mustang bass that he got new in 1976 or 1977 so I might be able to get you some measurements, too, if you need them. His son wants to start learning so he's starting out on the old short scale.
