RE: ENGINE FOR A SKYLARK56 MARK II
ST 45 will be great in that plane. Just go to a larger dia prop. I personally like the 11/5 or 11/6 on that engine. You may have to go to larger wheels for ground clearance. The 11/5 will keep the overall speed down and also give you some extra breaking power for landing. Do not over prop ST engines they like to spin (IMHO)
Goodluck
Brian