Got the old electronics working now! It was able to be fixed by adjusting the trimmer in the car on the left in your picture that controlled forward/reverse it's currently trimmed a little toward the rear of the car for the detent compared to yours. I tweaked it until the controller could stay neutral on trim and not spin the wheels either way. Thanks so much for that picture and description!

I also found some ABS to melt so I'll be doing the body repairs when I have some more dedicated time to allow for it to melt and use before becoming solid again (the glass jar i have is a bit large so not sure how long it would keep it liquid.