I put a 48 Plymouth business coupe on a 1st gen Dakota chassis.

I suggest you begin by parking to two side by side, then remove the sheet metal from the 1500 chassis and do some measurements. I suspect the 03 1500 is too wide, and has too long of a wheel base. The wheel base is usually pretty easily corrected, but if its too wide, that could be a problem. The location of the motor in relationship to the front suspension center line is another area that would be of concern, moving the motor/trans backward is generally pretty easy, moving the motor forward or the front suspension center line backwards is an entirely different matter. The relationship between the front suspension and the motor will likely need to be within a few inches of each other between the 46 Chrysler and the 03 1500. With the sheet metal gone from the Ram Chassis, with the two parked side by side you can move the chassis forward or backward to see how things are going to match up. You will know pretty quickly how big the project will be.

Also, a 1500 chassis sits pretty high off the ground, most street rods don't look so good sitting very high. While the sheet metal is off the chassis, you might want to see what will be involved with lowering the chassis.

If the measurements bear out, I wouldn't get rid of the cab or box just yet, you may be able to reuse the cab firewall and floor pan, and the box floor in the Chrysler with some modifications. The more stuff you can use from the donor truck on the Chrysler, the less money you will have tied up in the project. Even if you can reuse most of the stuff from the Ram, expect to dump at least $3,000-$4,000 or more in the Chrysler project.

When you get that sheet metal off the frame, post up a few pictures. Gene