Primo 65? When did that come and go unobtanium? The largest Primo I see on Paul's site is a Primo60, which has a 55" wingspan. Even at that, your Primo wing has close to double the area of karolh's Katana wings. Even at 7 lbs, that much area will certainly float. I've put a Saito 20cc 4-stroke gasser on a Mojo60 before... it's got the big wing like the Primo, and could handle the extra weight of that motor. I don't think an 8 lb+ bird with nearly double the wing loading would like that heavy of an engine, but maybe that's just my flying style too...
I think when I'm ready to play with 20cc gas again, it will be on an EE60, Ron Williams Sbach65, Mojo65, or the big Slide coming out.
-Case
ORIGINAL: acerc
If your worried about being too heavy this is my profile, a Swanyhouse primo 65''ws and it weighs 7lbs on the money and is a floater. So I think you will be ok at 8lbs.