Welcome to the board!
How wide do you need to clear whatever you want to clear? There is a lot of room between the rear frame rails, at the axle, on a 39-41 Mopar car. I don't have the exact measurements, but it has to be at least 45" between the inside of the rails. They are a lot wider then the od of a Dakota rear frame and they are 38" wide.

Look back through the pages on this section, there has been a lot of 40-41 builds documented here. I know someplace back in those pages someone posted frame dimensions for a 39-42 Mopar. I'm too lazy to look and would just get out a tape measure and check.

I know years ago I had the measurements all laid out to put a fwd Lebaran drive train between the front fenders of a 35 Plymouth and figured it would fit, struts and all under the fenders. The motor would have almost completely fit under the hood of the 35 and it is a lot more narrow then a 39-42. Gene