You could just call them. The number is 18009990853. Becauese you're going to use it for towing, I would recommend something smaller in the XR264H or smaller catagory, but you have a fairly high compression ratio for towing and you'll want to keep your dynamic compression ratio down at low rpms to hold off detonation. In that case, I would recommend the XR270H. Because the motor is a 383, it should lower the powerband of that cam a little so it might come on at 1200 rpm instead of the advertised 1600. All of these cams will require aftermarket valve springs be installed and may require the valve guide be machined to clear the lift.