I have a Yak-55. I fly it for the AWESOME aerobatics. It has a radial engine, part of the reason it flies so well.
I have an RV-8 that I built. I would never want it with a radial engine. The airframe was designed for a Lycoming, and silly me...I installed a Mazda Turbo Rotary engine. It added about 5 YEARS to the build time, and about 70 pounds to the plane. The extra 30 horsepower was nice, but 16 flight hours later I realized that 'engine development' is a full time operation. The engine cowl must be removed on almost every flight to inspect EVERYTHING.
I expect a ROTEC or VERNER radial might not require as much inspection, but the airframe mods will take away much of the 'good' of an RV:
-Good visibility over the nose.
-Good speed ratio, low stall speed/high top speed.
-Good proportion - The light weight radial will be mounted too far forward on a long mount.
-Good progress during building - adding YEARS to a build is a big drag, I know.
One RV-3 has an Walter LOM inline 4.
Which looks good. I appreciate different engine configurations, but they should match the airframe. Look at the Boeing P-26 and Grumman Wildcat; great looking radial engine single seaters have round fuselages.
Still, I wouldn't want to discourage a creative builder. Perhaps it would be a winner!
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing
-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)