Both the rear and front sumps were found on BB motorhomes from the early to late 70's.
An easy way to distinguish between the 2 is the drain plug - on the front sump it's located directly on the bottom of the pan and is in front; the rear sump is on the rear of the pan and up a little. The rear sump also has a port on the driver's side for a 90* fitting for the dipstick tube to screw into.
Rear sump first - this is one I sold awhile ago. Note the drain plug location, port on the side for the dipstick fitting, and the brass 90* fitting:
