Coin toss between the DLE and RCGF here. I've run the tar out of both of those. From what I've witnessed, the VV seems to be a good one as well. When it comes to support, the nod would have to go to DLE.

Beyond that, the 20's are pretty much going to limit your prop size to 17". If I were building something the size of what you're considering, I might want to go with something able to swing at least an 18" prop - which leads to the question of why are you considering only beam mount? A Zenoah G26 or even a G38 would do a great job without really over powering.