a OS 91 to 120 would be a great choice for any 60 size warbird in that wingspan and weight range.
overpowering it has no real benifit,as for a 70 fs probably a little less power than I would like but it would surely fly, I would say go with a 91,of the 4 60 size warbirds I have ready to fly 3 have 91 surpass engines,and 1 has a 120 surpass.