For those with experience with this engine, I would to know what size plane you are running the 58 on . Trying to decide what airframe to put around motor, I want good performace for all out 3-D, would it fly a 21# plane. I have seen some 33% planes that will come in at this weight the 58 will be on stock mufflers.

It would totally rock a 21lb plane for 3D.
Which 33% airframe are you thinking ?

I was thinking about a Aeroworks Extra 260 75cc. Would the Evolution 58GX2 be enough? I do not know but think it would be interesting effort to attempt. Here is what I was thinking.

Aeroworks 75cc Extra 260
Evolution 58GX2
8711's with Titanium links, standard on throttle
AR 9100 Rec.
A123's Fromeco Extreme, 2-rec 1-ign.
All Carbon tubes, main gear & tailwheel
Will it work I dont know, what plane are you flying with the 58, and AUW?.

I fly the 58GX on planes at 19 to 20# (27% Pitts Challenger and 30% Yak). The 58 will swing a 24x8 prop at 6400+ rpm using a pitts muffler (and more on a canister setup). Based on Pe Reivers' thrust calculation spreadsheet, that is 30+ pounds of thrust. I have heard rumors of 40# of thrust out of that engine. That should be plenty for a plane in that range