RE: Phoenix Strega motor for 120 class racing.
I have had several of the blocks split so if you already have the covering off it is a simple thing to cut open the balsa sheeting above the blocks and epoxy some wood in there to beef it up. The ribs are strong enough, it is the blocks that split. Check into that OS 120. I wish I could be more help with the big 2 strokes. I just haven't had much experience with them since they don't fit in our rules. There are a few 90 size engines that are quite fast and have a 60 size case. Super Tigre, Thunder Tiger, Magnum and OS come to mind. Thunder Tiger, GMS and OS make 120's. The GMS 120 looks interesting but I don't know anyone who has one. Keep us posted, I am interested in what you find out.
Blessings, Terry