[Shelbytexas]

I have a 68 Shelby Convert with a 550 HP / 600 Ft Lb Torque 427 (454). Gears are 3.50's. Currently Toploader close ratio 4 spd. Considering a 5 spd. Can anyone suggest which to go with given this HP / Torque rating. How much will it cost? How much time to change over? Will be used on a track / possibly Big Bend Open Road Race. Rpms at 100 mph are approx 5000.
Thanks!