My thoughts:
Either one should work fine, however- a coupler at the box will allow for some back and forth movement during use; you would need some sort of support brace and bearing on your intermediate shaft (coupling/adapter shaft between column and box) to keep things stable.
With two u-joints, I would think that it would be more solidly located; but with the later model column with the collapsible shaft, use may apply excessive force to the plastic shear pins causing them to shear, and allowing slop to be introduced there... So a support on the intermediate shaft would probably be desirable in this case, too. But, not a lot of room on an early A body for all that...
One way around this would be to use a rigid coupler at the box or the column,
and using just one u-joint or the pot coupler and eliminating any potential slop in that manner. Kind of like making your own adapter similar to the ones sold to adapt power columns to manual boxes, except the spline arrangement is reversed.
As you well know, space is very limited on the driver's side of early A bodies, so your arrangement of where the coupler and joint go (joint on column, or joint on box) is going to be whichever gives you the most room.
