RE: servo size and torque???
My Herr P51 says it requires at least 24oz/in servos. Even with the largest recommended engine it will fly much slower than your plane.
I agree with SST Dymond D200 servos (34oz/in) are more compact than hs81s or hs85s. The dymond has a much more robust gear train that is cheaper to replace. I've used them on dual aileron servoed .40 size high speed planes.
I have a number of HS85MG servos that I may use in even more demanding situations.
I like the Hitec Electron RX but it is a little pricey compared to the Cirrus mx4 or mx6 which will also do the job.