Richard,
If you have a 1 in a hundred Fox .35 go with it. But the plane needs to be very light 38-42 ounces for this engine / plane combination to perform properly. I have been flying the Max .40-H for the past three years and it is one great engine. In OKC I use an 11-4 prop in Pampa TX, 11-5. Also I have tried lots of different fuels and the best I have found is 10/15/8.5 (Nitro/Castor/Synthetic).
All of the engines from that era need the castor for cooling and the synthetic keeps them clean. I run some 10/22 Powermaster through it for a couple of flights about every 15 flights or so just to keep from gumming up but it runs too hot if I use this all the time. I am not trying to start a string on fuels with these comments just giving you the information from my experience. My Hurricane weighs 48 ounces and the Max is plenty of power. I also use uniflow with restricted muffler pressure.
Other issues: It is permissible to widen the fuselage to permit the use of commercially available tanks on the classic designs and this will give you the room necessary for the Max. I would use a 1/2" prop extension just because it will help with the balance and ease of Cowl construction. I use a "Veco" style tank: 1X2X4 which is 4 ounces and have to short fuel in order to not over run in OKC. You also should lenghten the landing gear about 1/2" in order to comfortably use the 11" props. I believe this is also legal for Classic as long as the gear exits from the original point but am not 100% positive about this.
Personal note: I assume that you have located Topping Park and become acquainted with the OKC bunch. I grew up there and flew lots of planes over many years at Topping. Lots of good guys in the area and I am sure they are/would be happy to have you in the group. Good luck with the Nobler project. Hope to meet you next time I am in the City.