The vent on top of tail shaft housing is a '70-up and vent tube on the side of case is pre-'70. The dipstick tube in the pan doesn't make it a 26 spline, the year does. All 70-up C-4s are 26 spline whether dipstick is in the pan or in the case. All pre '70s and most '69s are 24 spline even with dipstick in the pan. Over the years when the C-4s have been rebuilt, many were upgraded with the '70-up 26 spline direct drum and '70-up front pump(for the larger 26 spline input shaft). That has been a common rebuild practice for the old pre-'70 C-4s when being rebuilt so that's why some pre-'70 C-4s have 26 spline drums and shafts not because they came with them which they didn't. The only thing about pan fill C-4s that differs from case filled are they typically have better servos, some have hardened input shafts, and have over all better/upgraded internals for certain areas.