I don't know if this canister was specifically designed for this motor, they label it for 26-33cc 360mm x 47mm, about 6 oz. Comes with a 4" extension that can be resized to whatever works for you, so I doubt its a true tuned system, but it does work well. I ran a "recreation blend" fuel one of the local stations supplied, think it was 90 octane.
You can find info here:
http://www.hatori-models.co.jp/HP3/air-e.html
Sadly that motor lost the c ring clip off the piston retaining pin and seized the motor. What a bear to get that apart as it got lodged between the piston and liner. Had approx. 250 flights on it.
I've only got a couple gallons on my new motor, and was running a 19.5 x 11.5 last I flew it, which was last fall. It was turning 71-7200.
That's the muffler I bought for my GT33 and I don't think it was designed for the OS in particular, but I decided to give it a go.
Have you tried the 20.5 X 10? That's the prop I'm gong to try. I'm thinking it should give around the same RPM as the 19.5 X 11.5?
I'm getting that RPM with a 20.5 X 10 on my 185cdi, so if the 33 can get close to it using that muffler, it should be OK.