i would think the bellhousing is the main question point if it is a C-4. that bolts on though so its an easy fix
If it's off of the 200 he's also selling. It'll fit another 200. But if it's going on a 250 or 302 you'll have to change the bellhousing and convertor. If it's a 69 tranny, the front input shaft is a 24 spline. The 74 will be a 26 spline. So you'll need a new TC no matter what, I believe.
Remember, even if it's the same motor try to get the Torque convertor also as the one from your 74 will not fit the 69 tranny.