will new clutch fit bellhousing?

Dave NEO said
well t hat might be reassuring - so why does retainer bore size vary?

In 68 the 18 splines switched to 308 front bearing making a larger retainer necessary. In 70 the 23 spline a b/e body with 383 also went to the large bearing/retainer.

As long as the retainer matches the bell your fine.