Eric, Its not your 351M’s fault that it was born in the time of pitiful performance, but there is much help out there. Being a long time Ford mechanic my daily driver is a 79 Ranchero with a 351M, 3 speed FMX trans and 2:49 gears. Needless to say, acceleration in stock form on a good day, Escorts could show me their taillights.
It sounds like your motor is running well but the first thing is to get the cam timing where it belongs, and you will need a multi-index gear so the cam can be advanced straight up. Ford retarded the camshaft to help pass emissions back in the day. All the fancy intake and exhaust won’t help much without getting the timing up where it belongs. There are several aftermarket intakes and 4v carbs. out there, so the choice is yours. I am looking for MPG so I picked up an old Offenhauser Dual Plane intake and looking for a 500 cfm carburetor for it. A lot of people are dropping in the 400 crank but for me, more efficient 351 cubic inches is enough to power the my Ranchero easily, and I wanted to help performance and MPG without digging into the long-block too much. I went for the timing chain set, carb., intake, 1.8 roller rockers, MSD 6A, MSD coil, headers ( I got all these off ebay for less than $300) and dual exhaust. If your vehicle is geared like mine and you don’t do much highway driving, the easiest way to get your 4000 lb vehicle to accelerate would be to put some 3:50 gears in the back. I am keeping the 2.49’s and would like to go 5 speed to help with acceleration and keep good MPG. If the trans is working I’d leave it, maybe with a shift kit. The 351/400’s are also in desperate need of compression, but that is a complete rebuild and another couple of pay checks. Have a great day!!!