Tranny doesn't fit, now what

Most likely he has a 308L bearing retainer on a 23-spline. I'm also guessing an early bell which accepts a 307L bearing retainer. I would swap out the front case with one that uses a 307, or I would have a machine shop enlarge the hole in the bell to fit the retainer. Don't turn the retainer down to fit the bell.
Fun with 4-speeds.