What prop to buy for my GT-21?

[Lenny]

My 270 in the GT has a "new" 270 hanging off the back now. I have NO prop (s) for it yet. Left hand rotation, what do I buy? I have a 350 in it and "performance" and top speed is not an issue with this boat. I want to see 55+ gps when all is said and done. Pitch and Diameter and make please...1:61-1 ratio

Thanx

[Lenny]

Thanks for the reply. Do I assume this would be a 15 1/2" diameter? and what do you mean flo-torqe? I will count my splines when I get home.