I did a T-5Z swap in to my 70 XR-7. It is a 351W., but the fit is the same. The T-5Z is the strongest of the Ford T-5 line. My kit was from Modern Driveline out of Idaho. The company CougarCJ mentioned. I swapped the gears for a set of 3.50 with a Tru-Trac unit and love it.
I documented in this thread, https://cccforum.discoursehosting.net/t/so-i-am-planning-to-repower-ginger-this-winter-spring/4248/1