The side panels of the windshield are close to flat if not completly flat. I think you can replace with clear plastic or lexan sheet cut to size.
I updated my dash a few years ago. The orginal "wood grain" was faded and I replaced the dash panels (both upper and lower) with 1/4 in. oak plywood. I added about 10 coats of spar urethane and it still looks good.
I also updated the speedometers and other gauges and added a depth meter.