Frame mounts, mean the engine is mounted in the frame between the seat post and the front fork. They can be 2 cycle (premix oil and gas) or four cycle.
The rear rack mounts can be friction drive on the tire, or chain or belt drive to the hub or spokes. All of the "rack" mounts I have seen are 4 cycle, but there are a lot of 2 cycle weed wacker engines that people have arranged as a friction drive.
I hope I haven't explained it all to the point of confussion. )
Congratulations. I don't think any more, just replay 78s from yesteryear. ) Like my first engine rebuild in 1955. An army surplus 500 watt DC generator with a Briggs & Stratton Model I engine. Broken crank among other things. Remember it well, but not this mornings breakfast.
