I never thought about it that way, but yes .1 cu in per lb for a conventional 4-stroke is a good rule of thumb for adequate flying power. But I would make this a minimum for a warbird that needs to go fast to fly "scale". Since the full-scale Seafury topped out at over 450 MPH I would say that your model counts as one of these!

A 6 pitch prop is fine for a 40-size warbird, especially with a 2-stroke engine. But I've found that as the models get bigger and the engine RPM for the larger engines is lower (especially with a 4-stroke) more pitch is needed to get adequate flight speed. An 8 pitch on a 4-stroke sounds about right for your plane, I think that you would find that with a 6 pitch prop the 'Fury will look like it is just cruising along even when at full throttle.

Yes, there is lots of controversy on YS engines here on RCU. While I wouldn't recommend one as a first 4-stroke, if you have some experience and $$ is not a huge factor then they are ideal for warbirds. They put out tons of power for their size and have exceptionally reliable idles (and deadsticks on planes with retracts can be a very bad thing for obvious reasons). A 110FZ on a 12 lb warbird would be a great combo. But if you really just don't want to go there then the new Saito 125 would be my second choice.

Walt