Originally Posted by doxilia
The 61 V is OS's rear exhaust short stroke. The VF is the front intake version while the VR is the rear intake version typically used on boats and on fans.
Thought it might help.
Yes you are right, OS 61 ABC rear exhaust & rear valve ... but also used on early 1980's F3A airplanes too. Like the Olympus at the Pensacola 1983 WC