There are 2 types of fuel tank bodies.
#1 - M151, M151A1 & M151A2 Pre emissions system tank & #2 - M151A2 emissions control tank.
There are 3 types of complete fuel tank assemblies.
The M151 & M151A1 came from the factory with a electric fuel pump in the fuel tank. This is the 8" bolt in "insert" with 3 connections on the top. 1 - Fuel pump power, 2 - Fuel out of tank to carburetor, 3 - Vent to air cleaner. Separate from this is the Fuel level sending unit.
M151A2 Pre emissions used the same tank as above, but had a mechanical fuel pump, and the 8" bolt in insert 3 connection are as follows. 1 - Supply to fuel pump, 2 - Return for excess fuel from carburetor, 3 - Vent to air cleaner. Separate from this is the fuel level sending unit.
M151A2 Emission Control Fuel Tank, 9 different holes on the top of various sizes from 1/4 inch to 3 inches. A mess of steel tubes on top for the emission control. Fuel out & return and fuel level sending unit.
Pictures below will help sort out what this all encompassed and looked like. Also a detail of the fuel caps correct and usable on your vehicle.
M151, M151A1. Fuel Tank and connections. Original "factory" gas cap is different than pictured. See details in other pictures on this page.
M151 and M151A1 Fuel tank - 8 inch insert, top round device is vent, left square is fuel out to carburetor, right round device is connection for electric fuel pump.
Original Style Fuel cap for M151 & M151A1. This was disliked and modified (ears cut shorter or bent over) because soldiers would catch their pants on the ears and rip them. So they went to the cap pictured above, but this was hard to get off with no "ears" for leverage. So then the military went to the flat cap with (mickey mouse) 2 tabs. Seen is picture #1 & #4.
Replacement cap for M151, M151A1 & Ford M151A2 pre emissions. Correct cap for AM General M151A2 pre emissions
ORD # 11660517-1
M151, M151A1 & M151A2 Pre emissions Fuel Tank
M151 & M151A1 Fuel Tank