In the 82/3 model year, it was more than likely an 351M. We had an 83 that was a 351M, found out it was an 82 model year engine.... that had the Variable Venturi POS!!!!! I think it was part of the demise of that engine. DO NOT USE CARB CLEANER SPRAY in a VV Carb. You will soften the metering rods, which act somewhat like a choke.... We were headed out on a week long vacation on Kentucky Lake... and we did a tune up, plugs, cap, rotor (That is how we found out we had an 82 engine, the distributor was different than the ones in 83, cap and rotor did not fit). We cleaned the carb, and replaced the Fuel Filter, and took of to Kentucky. We got there fine, but while the truck sat, the metering rods stuck, and it was like driving with the choke closed. Limped it to a Ford Dealer in Benton, Ky on a Saturday morning. We told them what was going on, and the Good 'Ol Boy running the shop, got us in, told us what we had done wrong, fixed it, and sent us on our way.... and I don't think he even charged us $100. Ran fine after that, until the carb started to go south and dump fuel in... I think we would have more control of the fuel with a can on the roof and a hose into the intake.... We had the issue "fixed" a 2v from an older 351 was installed, with an older distributor that had the vacuum advance, since the 82/3 had a "brain box". Not sure what the HP rating was, but I know that old truck could pull a house. I think it had 4:10's and front and rear LS (The truck I was talking about in the Dana 60 thread). I know it had the power, if you were trying to move something heavy, if you had it in 4 lo, on dry pavement, it would just sit still and bounce...... while we had that truck, it your could get it to hook to the ground, it would pull it..... that truck had a wrist pin knock for the last 2 years it was on the road.... I was in college, and we did not have a lot of $$$$, it was rusting out and we had lost the splines in the joint to the passenger side on the front. So we just kept driving it.... it got Mom and Dad back home one last time... it died about 100 yards from the house, and Dad was able to coast it to the garage.... not sure what the actual internal damage was, but when you pulled the dip stick, I am surprised fluid did not run out.... there was "fluid" notice I did not say oil.... about a foot and a half up the stick, and the radiator was bone dry..... had 100,628 miles on it when it finally let go......
If you do a tune up on it, verify which rotor you have. The 82 engines had round "platter" rotor inside the distributor, the 83 engines had the typical rotor, shaft with a "lobe" that contacted the plug end. We had an 83 MY truck, with the platter type rotor, and the two were not interchangeable.....
I have not seen it in documentation, but from what I was told, the 351M (Modifed, or Mexico) had a Windsor Block, and Cleveland heads..... I do know over the years there were 3 designations for the 351, 351C (Cleveland Engine Plant), 351W (Windsor, Canada Engine Plant), and the 351M.......