It was never that common but used sparingly in Europe and North America in FC. From what I recall the biggest gains we made with the stock engines was by cutting a few rotary valves as from stock they do not have enough duration.
Pipe technology has come a way as well. And you can make gains trying some pipes.
The ignition was very good for it’s era and the case/cylinder design. You may be able to bolt on a new era BRC cylinder for more juice.
Neat cassette style transmission and light design.