RE: O.S. 61 SF vs. SF long stroke
17702 - 61 SF
17710 - 61 SF-P Ring
17712 - 61 SF-P
17801 - 61 RF
17802 - 61 RFP
All these engines use the same crankshaft OSMG 4561
The 61 RF Hanno in both ringed and ABC used the same crank which was the OSMG 4634
The RFN uses the OSMG 4630 crank
Enjoy,
Jim