Love the 1936 Plymouth. I have a 36 business coupe. Bought it in 1964. I drove the heck out of it in high school just as it was. The original owner had replaced the engine with a 1941, from the serial number. I drove it winter and summer. Girls always wanted a ride. I could beat 6 cyl. Chevys in the 1/4 mile and cruise at 50 mph all day. It would cut great donuts in the snow. Fast forward about 35 years......I still have it and cruise around town. The rear gear is 4.11 factory and 50 mph is about as far as I want to wind it up. I don’t take it out on the 65mph highway into Bend. The 36 is a one year for some parts. No one makes a disc brake conversion for it. No, not even Rusty Hope.
The rear brake cylinders are one year. I finally found someone making replacements on EBay. Also the front motor mount was hard to find. Finally, recently found that on EBay from Vintage Mopar. The U-joints are ball and trunion which are difficult to replace and spendy. I’m considering converting to a T-5 five speed, and a newer rear. This will require a new driveshaft with modern U-joints and a new bell housing. What you have is good and dependable. Just depends on keeping it original or improving highway drive ability.
Have fun!