CL scale has a limit of 1.25 cubic inches, when I convert the 20cc to cubic inches I get 1.22 cubic inches which would be legal. Most CD's would probably consider the gas engine has a 2 stroke engine which has the limit of 1.25 cubic inches.
The other limit to be aware of is the 20 lb limit, models can be flown that large but it does tend to be work out and make sure you have an adjustable line guide to keep the line tension within reason.
I have flown with a .90 2-stroke before, the sound of the gas engine would be impressive compared to the glow engine! My 1/4 scale Morrisey Bravo was 17 lbs and Grant's Spacewalker (1/3 scale) comes in at 19 lbs....no problems
Go for it!
Fred