I agree, your car is very unique and in very good shape. Just leave it as is. Basically a gear swap and better exhaust would have been my only mods to that car, might be even too much. As you said your 442 is your fun, fast classic car. My 88 was so mangled and hacked when I got it, wires cut all over and some burnt, earlier 5A 307 without the CCC system, all parts gone, no cat, at least had the factory aluminum wheels. I have decided to say scew the max mileage, will probably still get 20 on the highway, it needs to be more fun to drive, 1/4 block burnouts again. My Wife monopolizes our Challenger GT so I need to make my 88 fun enough with the 350 back in and 2300 stall, a fairwell tour while I make the 70S similar to your 442, with the 424 SBO, a car that goes sideways down the road with just the skinny pedal. Stock is only stock once and even louder exhaust will make everybody want to race it, so just leave if it makes YOU happy.