I fitted a high torque gear reduction starter on my 1980 C3 but ended up getting it from Ecklers USA . A straight forward fitting job to get correct gear mesh and lash with fly wheel ring plus no need for diode in the wiring harness as 1974 onwards don`t have ballast resistor or a points type distributor . Cost about £170 I seem to recall . A big improvement on the original `half ton` job and more air space around it as Daytona said . I also wrapped exhaust in that area for greater protection against heat soak too.
I got mine from real steel. Lifted in with one hand, tightened the bolts with the other.
One point however, there is no R terminal, so you will need a diode if your setup requires it.