I rarely enter into these types of conversations as they generally end up being a battle of opinions. However, I have time on this Sunday morning and want to comment that I agree with both Don and Scott's comments here. I have personal knowledge of a Corvair engine running in Zenith 601XL - and running well since 2007. I know this because I built it. It now belongs to a friend and has over a 1000 hours on it without any real issue, (other than the airframe issue the FAA set out to resolve in 2010...other subject).
The reality is that there are component failures in both certified and experimental engines - I know, I own a 1975 Beechcraft Baron that eats my lunch on a routine basis. Ultimately, this is experimental aviation and some experiments don't go well. But that doesn't mean you stop; a good experimenter figures out what went wrong, adjusts the formula and tries it again. With airplanes, this is the basis for Phase 1 operations and staying near an airfield in the event a failure occurs.
I believe the issue, especially with the RV-12, is that there is a majority camp that doesn't want to experiment, but rather build a highly reliable and safe airplane as an amateur - and that is the point of E-LSA. But there's still a contingent, myself included, that want to experiment with the design and still be free to talk about what we're doing and share our experiences with others and learn from them - enter VAF.
I'm building my RV-12 as E-AB and am installing a UL350 engine. I studied many available engines before I decided on this one and was very much for the Viking engine; ultimately, Jan was the deciding factor me as he was defensive and wouldn't answer my questions - and being the engineer that I am, I need answers. I think he has great ideas, but he's his own worst enemy.
The whole PRSU debate is somewhat pointless as the concept of high speed engines turning slow props through gearing has been proven for decades (Don, the P51 is a good one indeed); but so have direct drive engines. The difference is in the implementation; sometimes a good design is improperly installed and sometimes a bad design is well installed. There's simply too many variables to make such broad statements, such as "car engines don't belong in aviation".
Separately, the Austro AE330 engine, used in the new Diamond DA62, currently has a TBO of 1800 hours, but they have applied for 3000 hours to the EASA, which is pending. But that aside, what bearing does TBO have on experimental engines anyway? UL Power doesn't even list a TBO in my engine manual - and after talking with them, their basis is simple: most engines don't get flown more than 100 hours per year anyway, so the engine should be overhauled on condition. Leaks, due to age hardened seals, will tend to occur long before their cylinders and bearings wear out. What's more, TBO doesn't apply to part 91 operators anyway, so it's irrelavent (I'm surprised at the amount of private pilots who believe TBO applies to them). Sarcastically, how's that TBO on your car? A 2000 hour TBO is about the same as saying "overhaul your car engine when it gets to 100,000 miles". And that's silly; I have nearly twice that on my old Ford Expedition and it's running well - mostly due to good maintenance, but also a good design and construction. Automobiles and airplanes both rely on physics and engineering; good designs, and good constructions of those designs, combined with good maintenance make for long lasting vehicles.
As far as the Viking 130 goes, I say "have at it". It looks like a good package and hopefully Jan has the gearbox design worked out now.