RE: FP or LA
I have built, flown and owned many twin's over the last 50 years or so. Both the FP and LA are good dependable engines, and are surprisingly strong - although as mentioned earlier, they take many runs to break in, and you need to keep them on the rich side. The main thing you want with twins is reliability. Ball bearing twin needle carb engines are somewhat stronger, but most guys way overpower thier twins anyway. I have read and believe to be true, that two engines equal more power than if you doubled the two into one - in other words, a twin engine 25 would be equal to more than one 50 size engine.
One piece of advice i would give to anyone flying a twin would be - tune one engine slightly rich with a good reliable idle, shut off - tune the other engine the same way, shut off - refuel both, start and fly. Don't worry about exact sync, and don't try to retune one with both engines running. Guys get in trouble when they get both running good, run them up before takeoff, and try to sync by leaning one engine down - that's the one that cuts off on takeoff or when flying.
Here are a few of my twins i am flying now. The one wth 3 engines are OS 28 FSR's (20 + years old). The Twinstar is running two OS 25 LA's.