Is it possible to install the Ampeg analog preamp in to bass body preamp cavity

This would go well for you if you posted pics of the preamp and it's guts.

 

Well, I found a shot of the rear of the guts. It seems it is PCB mounted. What that means us you are pretty much stuck with the shape everything is in right now. The pattern of the knobs, buttons, switches and whatnot would have to stay the same. You couldn't put the knobs wherever you wanted. You would also have to figure out longer wires to get the battery out from behind it.

Seems easier to just use it as a stomp box.

 

You can take the pots/switches/etc. off and solder pieces of wire to their connections on the PCB, thereby allowing you to put them wherever you want them. The problem is that the PCB is pretty big, and it won't necessarily be easy to fit it in a bass.