This sounds like a fun project to play with. I hear ya on moving slow. While I am young at 58, persistent back problems are painful and limiting. Also, I’m no Rockefeller either.
3.55’s are tough to get great mileage from but for where I am at, mid Florida, speed limits around the area are normally + or - 10 mph of 45, 45 being the average. So my 3.55’s in my Magnum currently work out pretty good for around here. RPM’s are low due to the average posted speed limits.
And, I agree. I was a heavy mechanic for decades. Had a side biz as the neighborhood Mr. fix-it guy. Always in grease and oil. Everyone’s car runs and works great except mine. Too tired to do anything on it and I never wanted to since I was doing it all the dang time.
You MAY want to contact Dana a member here that rebuilds carbs with a good positive response from members here. IDK his prices but his work is often made a bunch here pretty happy.
He may perhaps have the carb you’re looking for. Ask him. Might have some luck. Who knows?