Yup, those dimensions are accurate to an original 1975 50 gallon tank. My new tank is currently in production, just got the drawings from RDS today. I did slightly modified the original tank height to an even 8". This made the tank 45gallons instead of 50gal. The reason I did this was because the old tank was laying flat on plywood and it only left about 1/4" of clearance from the top of the fill and vent tubes to the bottom of the hatch cover. I plan on raising it off the plywood to allow air flow and I didnt want to run into problems with the cover hitting the top of the tank.
I would try to get a hold of seabob4. He hooked me up, and might be able to do the same for you.