I just put a 8ba in my 40, I had to use the 49-50 Merc pass. pan. The truck pan with the large clean out would not fit. Probably because of my dropped axle. I also used the wide truck pumps without a spacer.
I think the long sump pan was used in the 1953 pickups. They are not common. The center sump types were 49 to 53 Ford car and 52 to 53 Mercury. Most 49 to 51 Mercury sumps have three studs on the back of the sump to attach the starter plate and keep the half bell more stable. In the late 51 Mercs, they changed the bellhousing to a full unit and also started using the Merc-O-Matic more so they deleted the three studs.
The truck pan with the clean out is deeper than all the other 8BA pans but it is a rear sump.