No factory overdrive for that specific truck. How ever an E4OD from a later 460 will bolt to the M engine. Would need an aftermarket controller and fabricate mounts for the transmission.
if it is the stock engine then it is not a 351m because ford had stopped making the engine before 79
Firing order is : 1 3 7 2 6 5 4 8
of course.
For a 351m engine the oil sending unit is located on the top of the engine between the carburetor and the firewall.
the 351M/400M Ford motor has the big block bellhousing bolt pattern, like the 460 and 429 engines. So any overdrive transmission would need to have the Ford Big Block bolt pattern or you will need an adaptor. I do not believe Ford built any overdrive transmission for the Big Blocks. So I don't think there are any direct bolt ons The Ford AOD is a Ford Overdrive transmission that may be used but an adaptor plate and other modifications will have to be made. The GM 700R4 is a good overdrive transmission but would definitely require an adaptor plate.
not very much
Engine oil capacity, 5 qts with filter change.
need to know the spark plug gap for a 1979 Mercury Grand Marquis with 351 modified.
1-3-7-2-6-5-4-8
Google search - 351M vacuum diagram
Only if the cross member is in the way.
That all depends on when it revs. It could be your cruise switch. If you have a manual transmission, don't use cruise until you're in high gear. If you resume and try to shift, the cruise will rev the engine even when you clutch.