I know this is an older post, but since there was never a definitive answer given I thought I would post this here.
If someone wants to put a Peavey G-Bass neck on a Foundation, It will fit, but is not a direct bolt on. you would have two options. Option 1: use the two mounting holes closest to the heel and re-drill the two holes in the neck closest the headstock. this will leave a gap between the body and the neck heel (but would mostly be covered by the fretboard over hang) and the bridge would not need to be moved.
Option 2: Re-drill all four neck mounting holes in the neck and move the bridge a half inch towards the end of the body (If you notice a foundation body has room to do this)
Using a bridge with a larger base plate, like maybe a Badass II would probably cover the old bridge mounting holes. this would give you a nice clean neck fit and would be the option I would prefer if there were no plans to change it back.
here are some crappy cell pics of mine done in option 1 (didn't drill any holes though
) just to see if it would fit.