Which transmission and converter do you have on hand? If it's B/RB stuff you'd be money ahead to stick with the 383.

A mild 383 and 5.9 Magnum are going to be very close in power. For some reason the 5.9 has always been a gas hog.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon