Ed I think the 1.20 would fly it fine. It is not going to have unlimited vertical but Mustangs are pretty sleek and you should get good speed out of it. I had a kit built P-51 back in the day from GP that was ST .90 powered. It was plenty fast.The DLE30 or DLE 35RE would be more powerful, but the physical size of the 30cc gas is night and day different compared to a 1.20. The DLE 20 uses the same bolt pattern as your OS but would not have the power. Look at a 30 or 35 before you buy one. They are huge side by side to a 1.20.

David