Though never a warbird, I've installed a few 10's in cowled sport planes. Some were pretty "compact" installs (read that wadded in!), requiring some patience. Just remember to consider that when using one of these engines with a pumper carb, your gas tank is not only smaller (1/2 the size of glow), it can be located back near the wing tube/spar. This clears up a ton of room right in back of the firewall, possibly enough for your ign. module and throttle servo.
As far as the 8 vs. 10, there's so much parts interchangeability between them, I don't see any advantage to the 8. I don't even know why they introduced it myself.
Bottom line, if they're recommending a .45-.55 glow. I'd go for it. -Al