727 pump covers are the same. Early and late have differnt style vents , but thats it. Its the pump stators that are differnt.

62-66 uses a 19 spline input shaft and a narrow bushing on the front drum.

67-70 uses a 24 spline input shaft and a narrow bushing on the front drum. Both the 62-66 & the 67-70 you can not use a aftermarket billet front drum. As all billet drums use a wide bushing.

71-77 and 78 & up non lock up, uses a 24 spline input shaft and a wide bushing on the front drum, and can be used with billet front drums.
71-77 uses a 2 ring input shaft
78&up uses a 2 ring input shaft and 1 ring on the rear drum.