This was my plan, using a mid-90's Ram pump (since I'm running a Magnum, makes it easy). I had to make a threaded flange on a lathe though, and I will eventually weld/braze it to a new tank. Access port in trunk, done.
That's always been the issue. You have to put a lot of fabrication into making it work.
This E-Body pump seems to fit the stock A-body tank and is readily available only $120 more than a new sender.
What would really be nice is if Holley came out with Mopar versions of their in-tank pump modules. Their design integrates a 58psi regulator right off the pump, making plumbing and parts less complicated.