Put 80 flights on one this year. Mine is powered by a OS 1.2 4cycle, with Spring Air retracts, and flaps. Mine started with a K&B .65, Reliability forced me to my old stand by Super Tigre S-61. It flew fine with the S-61 (it flew on the wing) but on landings I did not have enought prop past the cowl to make an affect once I was flaired and adding throttle to lighten the touch down. I had a 1.2 on the shelf so I put that in it and it was perfict all those bounced landing were gone. AT-6's have a tendency to bounce on landings if not wheel landed but with the OS 1.2 $ cycle that has been saverly reduced.
In the kit they give you landing gear mounting blocks that are made of marine ply. I epoxied them in but in these bouncing fits it would have (on the occation when I screwed up a landing) the mounts would break out. The epoxy bond would hold the glue joint between the layers of ply would fail. I ended up putting maple in its place and that has held up great.
The firewall is all Lt ply. Re-cut those peaces out of marine ply if you plan to put a big engine in it. Fiberglass cowl is a must, the plastic one will start to crack appart after about 20 flights
With the OS 1.2 4 cycle and flaps at 8.5# my flight envelope is 110-93-25mph, that is about 110 mph in a full power dive ( not recommended), 93 mph top speed level, and a dirty stall speed of 25mph. All but the level speeds are estimates, the level speed was checked by the local constable.