Hello Montoya, I am also building a large scale prototype drone specifically for the Allison 250 B 17.
Engineered by a few ofthe best.Presently I have a completed rolling airframe in need of a turbine. Just for the record my design speed is 400 mph, empty weight 1750#, pay load over 1500#, range 1600 miles +.
The wing isa high lift lamiter flow type wing some where between 26' and 32' depending on performance. This does not mean that the wing couldn't be longer for other uses.
Your best bet is to find anold run out turbine. $10,000 good luck.
Worry about cooling the hot section if you use the pusher configuration.

Rick