How about the same combination that Plastic Soldier Company do? SdKfz 138 Marder III and SdKfz 139 Marder III. The early Marder in particular is a very popular vehicle with modellers.
To do a Marder III, we have to start with a standard 38(t) chassis. We are studying the different variations... there are at least 2 versions of the driving sprockets, 2 running wheels, and up to 7 idler wheels... Easy to do it in 1/100 or 1/72 scale; but in 1/56, you will need to put in a lot of thoughts! Also, PSC tend to "forget" some variation detail differences, which we know YOU will definitely point it out to us after we release our 3D drawings (if we were to do one)!
Being that said, we are seriously looking into doing some more early war vehicles for the axis and allies next year. So don't be surprise if there is a 38(t) or Marder III included.
PS: Your comments are always welcome!