Ｔｏ　ａｎｓｗｅｒ　ｙｏｕｒ　ｑｕｅｓｔｉｏｎ　ｉｆ　ｔｈｅ　ＨＳ－６３５　ｗｏｕｌｄ　ｗｏｒｋ，　 Ｉ say maybe for a short time. I would not risk a large gas airplane on questionable powered servos. I did use 2 HS-635 servos，one for each elevator on my 25% Katana for several months with no problems. If you are so short on funds I would not fly the P-40 and wait until I have the money to get some decent powered servos. In many of my larger scale planes I have been using some of the older 1/4 scale servos with very good success. I got them for next to nothing. The problem is that they are a bit heavy and slow, but for scale usage they seem to work fine. And in the 30 years of using them, I have had only one go bad.