Dodge Repair: Gas tank replacement

Question
I have an 82 Dodge B250 van. 318 V8. I needed to replace the fuel sending unit in the van. New unit is longer then old unit. Gas tank is plastic not metal/steel. No longer have old sending unit to refer back to for replacement. Want to order new tank, but am skeptic which is why I'm here. Old plastic tank has hole on top for sending unit insertion, hole/hose on side for fuel inlet. The new tank pictures show no hole on top for sending unit insertion, one hole for fuel inlet on side (typical) but on opposite side of inlet is a hole with lock nut markings for sending unit. The Haynes repair manual shows and reads the sending unit on top of tank. I am confused about this purchase I need to make and my question is this; with the repair manual and existing plastic gas tank having the fuel sending unit on top, why does the new 1 I need to order have the hole for the sending unit on its side?

Answer
Hi Alfred,
I appreciate your situation. Unfortunately I don't have any manuals for vans from the '80's and also no personal experience. Maybe a dealer parts counter could help. Is there a chance you could find one at a wrecking yard? The yards now have a nationwide hot line to locate vehicles in inventory.
Roland