Marc,
I'm stuck in O'Hare. If I ever get out of here and back home sometime next week, I can work out the details, but a 365 gr bullet is darn short, and a 20 will be more than enough by a pretty good margin. An 18" twist will stabilize a 550 gr 1.45" bullet at slower velocities for a long ways (like 1000 yds). The 20 will do the trik in a pinch.
I'll work out the details early next week if you wish, but 20 will be fast enough. A better question is if it is TOO fast. I do not know what normal twists were for the old 450 bpe with these sorts of bullets. I'm guessing upper 20s.
Brent