ORIGINAL: Flying Fox
Perhaps by using 4 magnets the entire engine could be removable to allow access to the real engine and battery/servos/receiver beneath. Will have to wait and see how it turns out.
Getting to use anything like a "full" (or even "half") dummy inline with a gas/glow engine will take some doing. You're only options are to mount the engine inverted (in which case it sticks out the bottom) or sideways (in which case it sticks out the side). Personally, I wouldn't risk trying to one of the RCV SP series engines in this sort of enclosed cowl. I thought about it for my CI but decided to go with the more reliable CD series. The reason I asked about electric is that it does easier to build a dummy engine AROUND an electric engine.
I am awaiting the outcome of your cylinder mold experiment. Hopefully the cast will cure. I have never done this either so I guess each of my cylinders will be done by hand, individually with some replicating process and jigs to keep me sane. Gianfrancesco is certainly an expert source for information and inspiration isn’t he.
I think the silicone will eventually cure, but there's still no guaranteeing that this, my first attempt at casting, will succeed, in which case I'll need to somehow acquire more silicone. If it weren't that I feel I really need to add casting to my modeling skills, it would probably be simpler to have just made the 6 cylinders one by one using the disk method (and this would have been super simple if I had had the disks laser cut). But the prospect of cutting out all those disks after doing all the flanged for the Hazet radiators just seemed like too much.
Anyway, you've certainly picked a serious project. I think you'll find that the dummy engine will be just one among dozens of serious scale adventures on this build. Have you already given some thought to how you'll manage 1/6 scale lozenge covering? BTW, I also have the Mizer plans (and also experimented with enlarging them to 1/4 scale).