Does anyone make an adapter that will work with(attach) the stock torque arm and a powerglide trans?

Third gens doesn't use a torque tube. It's a torque arm. Same idea, different component. You need to move the torque arm mount off the transmission and onto the crossmember. The easiest way to do this is to buy an aftermarket torque arm with crossmember for the transmission you intend to use.

Check out www.spohn.net for a PG version.

I had ladder bars and now a 4-link with my Powerglide.