To start, use the 4 feet 8 1/2 inches between wheels, as that's standard track gauge. The only other suggestion I have is to locate an old Alco unit with similar trucks and measure the demensions.
CSX railfans are how tomorrow moves!
Future owner of HSM Co Transportation- Rolling into the future.
"If I could return to those boyhood days of mine, and that green light on the Southern, Southern railroad line."