You're 25 hp too high. The P&W R1340 is rated at 600 hp. I've got a little over 1,000 hours sitting behind that engine on a B model Ag Cat and 301 Air Tractor. That and the R985 (450 hp) are probably two of the best radials ever produced. Just like any other radial though, they are finicky, and must be cared for and fed correctly.