I put a 36cc Brillelli on mine. I can't remember offhand the weight of this engine, but I'm thinking it is about 3.5 pounds. It is a fine power plant for this model. Unfortunately, Brillelli is no longer in business.

My Decathlon weighs just a tiny bit under 19 pounds. The reason for that is two extra servos for the flaps I added. An extra servo for a tug release and an extra servo for a bomb bay/drop. There's 8 ounces right there. I did a Smart Fly power system... another 4 ounces. So, I hit the upper end of the weight range. I used a composite LG, which is not CF and is heavier than the stock aluminum. So, there's my extra weight.

Most of this was slightly rearward of the CoG. I wound up putting my ignition batteries up front and am in front of the most rearward CoG suggested in the manual.

BTW, I really like the flaps. Perhaps being on the heavy side is the reason for this, but when landing the model likes to drop when it slows. The flaps make a big difference with this. I'm still figuring out the model... maybe 10 flights now... but I've started using about 1/2 flaps for takeoff and it seems more docile there as well.

As for engines. 60 ounces sounds pretty heavy. I would stay light if I were you. The main consideration when selecting an engine is the cowling. It is not very wide. A Pitts style muffler is a really good idea. With the Brillelli I wound up with very little cutting. The carb is a side mount which angles down a bit (engine inverted) so the top of the cowling is uncut, only the carb hole in one side and I had very little cutting on the bottom... muffler and spark plug cap. I am extremely happy with the combo. I think I'd look at the RCGF first. I'm not super familiar with that engine, but it seems that they generally are not wide engines... maybe rear induction? You have about 6" to work with.

There is one thing that I wish I had done. I did not use the doubled firewall engine mount. The engine bolts conflicted with the secondary mount... it just wouldn't work for my install. I do wish I had tossed the firewall material (light ply) and used aircraft grade plywood. The light ply is pretty spongy. I've compressed the ply badly in order to finally have a secure engine mount. This of course weakens the ply. I just can't bring myself to replace it, but I might eventually need to plate the inside with a layer of good ply and the outside. The only issue here is the top engine t-nuts are no longer accessible. So, it's not a great situation. It would take some work to make the firewall during the build, as there are few notches and such, but I would most certainly consider something to make this stronger.

Other most important mods included making a slide out tray for the gas tank. Tygon gets stiff over time and must be replaced. Even if I did glow, there is just no way I would ever build a model where the tank couldn't be removed. I made a couple of little wooden rails and used 1/16" aircraft ply which slide into notches cut at the bottom of those rails.There is not much clearance for the 24oz Dubro tank, so you can't go very thick with whatever system you use.

I had my Decathlon at a Giant Fly In Saturday. It got a lot of attention. I made me feel particularly good with my build and colors. After all, this model looked pretty small out there as it was not far over the 80" wing minimum for flying. It was extremely windy.... 15 to 20 mph winds which were relentless all day. Pretty much everyone was not looking so good during landings. I hadn't flown this model in winds that high, so I had my fllying friend take it up as he is a much better pilot than myself. We first made a bomb run and dropped two dozen plastic Easter eggs on the runway in front of the stands. Got a nice applauds out of that. There were about 4 planes in the air at the time. The announcer described the different models for the crowd... Then I heard him pointing out one 3d bipe doing a pretty shaky KE. It was a day when such things were not easy due to the winds. So, I started giving my flying friend instruction... LOL!!! Me telling him what to do. Well, I knew the Decathlon could do it and I knew he could do it. So I told him to slow it down, roll it over into a knife edge. This put it into a very nice high alpha KE. Well, his skills kicked in from here. The runway there is 1000 feet long. He got it locked in, slow... about 20 feet above the runway... and did a most perfect straight and level KE for the whole distance and carried it out about another 500 feet past the end, where one has to pull out due to trees and buildings. We here all know of course that this IS and acrobatic trainer, but few in the crowd including the announcer knew that. There was amazement in his voice and another round of applauds.

Yes, the model is a really fun model. Mine really likes to be tossed about. It really likes rudder in turns... not just an average same 'ole flyer. It is making me a better pilot... forcing me to use all controls frequently during each flight. Simple aileron turns aren't very pretty unless you like to see the tail hanging down on turns... then again, I am still behind the central CoG setting, so this would be exaggerated a bit on my model. It does nice rolling circles... although I can't do that yet. Loop, rolls, rudder turns, inverted flight and KE are all in its arsenal. I'm looking forward to continuing with more flights, better figuring out how to fly the model and letting the 'acrobatic trainer' teach me how to do either new things... or do what I do with smaller models really well on a big model.