Newer SA 4 speed has more potential, as I read the specs 28 hole hub shell takes the classic AW cog 13t , and is 120 OLD..

I have a BSR 3 speed 54: 15, added a 2 speed geared crankset 3 low range gears run though a reduction gear
between the pedals and the chainring

so pedals turn 2.5x faster.. my 54t acts like a 21.6t [50, 20 is even numbers, if you prefer]