Yeah, getting rid of those downdraft webers would help. I like and run webers but the 3 sidedrafts are the ones to have. My friend had a 72 240 that was mostly stock, except for a header and the distributor was converted to electronic, he had a set of SUs that needed a rebuild but decided to use the downdraft webers. They absolutely killed his top end, thing would pull decent up to 95-105 range then it fell flat on its face. I finally talked him into rebuilding the SU's and putting them back on. With the only change being the SU's he was able to pull harder up to 120-125. Thats not much faster but that's about all these cars will do stock, or close to stock. Alot of the limiting factor is low hp and torque, but the aerodynamics are not very good and make it even harder to go fast - I'm sure you could feel how much lighter the front end gets around 100 mph.
You can go alot faster is just takes time and $$$.
Matt