I'd second what Jim said.

I'm not personally familiar with the SK .80, but by reputation they are powerful, reliable, and are especially designed for higher torque rather than higher rpms. I'm told they're not screaming fast racing engines, they're more designed for turning larger props well. I'd expect the SK .80 to turn a 14x6 or 14x7 prop strongly.

Your Alpha .60 trainer would fly quite well with any decent .46 ball bearing 2-stroke on the nose. Not only would the power of the SK .80 not be needed on the Alpha .60, but the nose clearance of the airframe would make installing the proper propeller for the SK .80 a challenge.

I have a Super Tigre G-61 on my Sig King Kobra. It's fairly heavy, 26.8 ounces w/ muffler according to Tower, and it spins speed props really, really fast. I have a Master Airscrew S2 Scimitar 11x7 prop turning around 13,500 rpms on it. The Super Tigres aren't known for turning larger props well, although the mileage seems to vary greatly in this regard. I haven't tried a larger prop on mine yet, it's broken in but doesn't have too many hours of run time yet, so I haven't experimented with it.

The O.S. Max .61 FX is known as a fairly anemic .61 2-stroke, but it's a really good fit for the Alpha .60. It weighs almost a quarter of a pound less than the Super Tigre G-61 at 23.6 ounces with muffler. It will turn a 12x5 or 12x6 2-blade prop efficiently, good sizes for an Alpha .60 trainer. It's reliable, it's easy to find parts for it, and while it may not be a powerhouse, it will also fly the Alpha .60 really well with plenty of performance.

All three of the engines you've been offered are terrific. The O.S. Max .61 FX is simply the best fit of the three.