Hello Rick and welcome to the forum.
I am also a model flyer and I have built a couple of engines for flying models. I should say straight away that neither have flown yet!
One (15cc opposed twin) was significantly more powerful than expected, so I will build a smaller version.
The other (10.5cc V8) needs a lot of running in before I build a model for it.
I am currently working on a design for a 35cc 9 cylinder rotary, which at 5" overall diameter is approxiamtely 1/7.5 scale and will look like a Gnome, but internally very different.
What sort of dimensions are you looking for? A 1/5 scale Wright R540 is almost twice the size of a 1/5 scale Pobjoy!
The Morton M5 is about 7" diameter, so approximately 1/5 scale for a small radial.
Of course, you could scale something like the Morton to suit your needs.
If you haven't built a miniature IC engine before, I would recommend building a single first, to get a feel for the techniques and fits required before investing many hours in making 5 of everything.
Model engine drawings don't generally come with tolerances and GD&T. It is up to the individual machinist to decide how things should fit.
Pete.