Thought it was easier to just ask rather than go through google and its 10,000 hits. Have 70 Mach 1 with a 351 Windsor my uncle gave this firing order just wanted confirmation as he was drunk 1-3-7-2-6-5-4-8
The firing order is going to depend on what cam it has. You really need to know if it has the factory cam or an aftermarket cam. If it has an aftermarket cam, the firing order is probably going to match a factory 302 firing order. Most aftermarket cams have the original 302 firing order, I guess since 302's are somewhat more common than 351's. If your not sure about the cam, you could pull the valvecovers and watch the valve sequence as you spin the engine by hand. I'm not an expert on cams, this was just my experience when I rebuilt my 351 a few years ago.
I believe it is the original factory cam, I got the mach from my dad who is termianlly ill, the radiation fried his brain so I cant get any more info. I'm not that mechanically inclined though, I'm learning though. I would like to learn and work on her myself, have that love/hate relationship that my dad had with her. He said it ran when he shut her off but that was 4-6 years ago! My uncle used to work on her when she was racing so I do trust him, he said it was the same firing order as dads other stang, a 76 Cobra II with a 302 HO. My uncle gave me a mini class last night, the firing order is what he said, I went to check the timing and I think it is off but who knows might not be doing it right. We installed a new starter assembly, battery, cables, plugs , she has sparks she doesnt want to rumble though. We sprayed some ether in her and it was almost there, until my fiance put too much in and got flames, cut the engine and ran. But I really think she was there, could the timing stop her from starting all the way?? or was thinking it could ignition module?