What size torsion bars for a 383 in a 75 Dart?

a 1+ inch bar with a big block will be far from harsh. hell its not even harsh with a small block on the larger bars
No, not saying that. I would expect with more mass in the front end of the car a higher spring rate would be needed.

Im just saying if you like the feel of your ride now, no need to change it. If it is to soft go bigger, but just like the dopes who cut coils out of their coil suspension to lower their cars and end up shaking their livers out of their bodies, you can go too far. I dont think that 1 inch is too big.