khodges,
Many thanks for my pending induction into the hallowed Waco Brotherhood. Trust that I'll flaunt my membership relentlessly to my fellow modeling buds! By the way, thanks for letting me know that there are no additional hoops to jump through for this honor. At my age I have a tough time remembering car keys let alone a secret handshakes, et al.

Seriously though, I have to tell you that I'm flying my personal Waco SRE with a Saito 1.00 four-stroke. In my opinion, this engine is just about the perfect powerplant for the Waco and it is indeed featured in the Assembly Manual as the engine of choice. I can cruise comfortably at about 1/3rd throttle or so, at nice looking scale-like speeds. At full throttle, the airplane will pull just about any size loop you'd like. Icing on the cake is the wonderful 4-stroke sound coupled with the look of the model - for me, it's a genuine symphony for the ears and eyes.

I do not have either a G-20 or a G-26 to measure or weigh so I would be uncomfortable "guessing". But I can tell you that I am swinging a 15 x 6 prop on my Saito 1.00 and probably getting something like 9200 rpm or so. The Saito 1.00 - complete with the flex header and stock muffler - weighs 20 oz. I can also tell you that I did not have to reorganize anything in the fuselage to achieve the suggested 29% CG location. I can also tell you that the practical inside diameter of the fiberglass cowl is 7-1/2" and the distance from the firewall to the rear surface of the spinner backplate is 5-1/2". I would think that this information would give you some idea as to what will and what will not fit into the cowl. When I was setting up my Waco, the big deal for me was to try keeping the cowl as free from further openings as possible. The Saito 1.00 installation only required two small elliptical openings for the valve boxes and a small diameter hole for the needle valve extension. This left that beautiful cowl looking just like it should.

I hope the above information is of some help.
Scott