I have an RV6 completed in the year 2000 with an angle valve engine. It has 1500 hrs on it now. When I bought it the Sam James cowling had cracking near both front cylinders from interference during engine movement. I have since modified the cowling slightly (bumped out) to address that issue which worked great. It is hard to detect the bump out areas unless I point it out. It also has the Sam James plenum. CHT were always reasonable, oil temps were not (I also live in Phoenix, so that did not help!). The cooler is mounted on the engine mount behind the #3 cylinder with a nice transition duct. It had a 10599 SW cooler when I bought it. I have now switched to a larger dual pass cooler from a Seneca in the same location which is working well. Last year I installed transition ducts on the #2 and #3 cylinders to address the zero fin depth areas of those cylinders. I also removed sheet metal "dams" that were installed on the forward facing fins of #1 and #2 cylinders. My #3 was always the hottest on CHT. Those two changes made a big difference on #3. With those changes it was almost running too cool this winter but I resisted blocking off some of the cooler (lazy mostly) and just ran closer to peak that I normally would to keep oil up to 160 deg F. Summer is coming, but I am confident the cooling is well sorted now. It has always been manageable in the summer, but it definitely needed management.
So my conclusions on the Angle Valve in the RV6
Pros - Horsepower is fun, fantastic ROC, virtually no DA concerns, higher speeds possible, unique
Cons - Heavier airplane, W&B will need to be carefully looked at, cylinders will cost way more when they need replaced, cowl fitting likely needed, engine cooling may take some work.