The current OS 32 is the SX. Prior to the SX was the F. Prior to that was the 28 F I believe.
There was no SF version of either. Both the 32SX and 32F are excellent engines.

The 32F was available as ringed or ABC (ABN) for Helis but only ABC (ABN) for planes although you could easily convert the plane version to ringed with the right parts - same with the 32SX.