I would say the balance point would be at the main wing spar. However, the Corsair has a real long nose on it ... the Corsair was referred to as the "Hose Nose" in WWII because the nose was so long. So you may have to take the extra long fuselage between the wing leading edge and engine into account.

Wikipedia has this to say about the long nose on the full-scale Corsair:
"In order to keep the fuel tank close to the center of gravity, the only available position was in the forward fuselage, ahead of the cockpit. Accordingly, as a 237 gal (897 l) self-sealing fuel tank replaced the fuselage mounted armament, the cockpit had to be moved back by 32 in (810 mm) and the fuselage lengthened."

Which version of the Corsair do you have? Here's what an old RCU thread about the Top Flite Corsair had to say about the Hangar 9 Corsair:
"I am aware of the sensitive CG from a couple of friends that have the H9 version and experienced, in one case, disaster. The other guy was suspicious of Hangar 9's suggested CG, did some investigating, and moved it forward substantially."

Another poster in the same thread said: "Try to keep the weight down and DO NOT FLY it with the slightest suggestion of tail heaviness". Well, that's good advice ... but first you have to know where the CG should actually be before you can remedy any tail heaviness.

Since I have not actually built/owned a Corsair ... I think I better bow out of this conversation and defer to those who have actually built one. But I'm guessing that you'll need to find the location of the wing spar and place the CG somewhere in that vicinity ... possibly between the leading edge and the main spar.

But like I said ... don't listen to me too much! I could be totally mistaken!

As for servo's I would use Hitec 645MG's. What servo's did you install in the plane?

Good luck!
oliveDrab