Need exhaust manifold stud size for GM 3.4l (vinF 'LNJ') motor. This is a 2006 Pontiac Torrent AWD. Currently in process of replacing head gaskets (o joy - NOT!) and need to replace old exhaust studs/nuts. The (possible) problem: this is not the original engine so there is a question of fit. I've checked RockAuto and Amazon. Both sites say my engine takes an M10-1.5x62mm stud here. BUT the ones I took out measure approximately 51mm long, have a thread pitch of 1.25 and look more like an M8. + 6 each head. So : what to order?
Thanks in advance for your input.

I think you're going to need to take the best stud and nut that you have and go find generic units from Napa or the like. I don't see a kit out there for this, and we're suspicious that this is not the original unaltered engine.

Personally, if it were me looking to confirm size of these, I'd wire-brush the threads on a good one, then take it and a good nut to Home Depot and see what nuts fit the stud. Once I know that, I'd see if the same size bolts fit the used nut. Then I'd buy something from the tool department that I know I don't need now but imagine I'll need soon.

Remove a good one and match it up.

I literally laughed out loud at CathedralClub'* comment "Then I'd buy something from the tool department that I know I don't need now but imagine I'll need soon. " cuz it sounds so much like what I do all too often.
Thanks so much for the comments and advice, guys. Appreciate you taking the time to respond. Dug out a caliper to confirm my guess of the studs I removed being M8 and indeed, they are.

whoops, sorry I mis-spelled CathedralCub! That'* what happens when you have glasses but are too afraid of damaging them to wear them......my apologies.

LOL no worries! That'* actually a common misspelling of my handle.