212 Tillotson shaft bolt size?!

[dirtrider998]

Hi, I ordered a mega moto 212 complete kit with stage 1 tillotson from gopowersports. I had a very damaged box missing parts, waited for replacement parts, still some were missing and got the rest replaced.
Now, when installing the torque converter onto the engine main shaft, my stock bolt seems to refuse to come out. I'm talking about the bolt he installs at this point The stock one I can't get to back out even with a torque gun, it doesn't strip the head but it just doesn't budge, and I see from the video it's not reverse-threaded. Maybe my battery nut driver isn't providing enough power but I've used it on a ton of projects and it seems to have a lot power, and I don't want to chew up the shaft by grabbing it with toothed pliers and a breaker bar but I guess I have to? Also, the stock bolt seems to be different than the one he installs because the stock one has a flange/washer built into the head and the one he installs in the video doesn't and also has a split ring added and is likely longer to accommodate the torque converter. I must be missing that bolt too, so I'm wanting to know the size and thread I should use for that so I don't cross thread it and mess the whole thing up. thanks. I tried searching things like tillotson 212 flange/crack/shaft bolt size but found nothing. If I get the stock one out, I can bring it to the store's thread checker but that thing is usually cross threaded to hell. thanks.

 

[dirtrider998]

It's 5/16-24 FINE thread, NOT 5/16-18 more common in store bins.

I was able to get the stock bolt out with a giant channel lock with rubber sheet wrapped around the shaft and a breaker bar. Come to find it says 5/16 right on the bolt head (but not -24 or -18).
When I used Lowe's thread-checker it's not the more common 5/16-18, it's 5/16-24 and luckily that port apparently doesn't get used much because it wasn't cross threaded/damaged/questionable. 5/16-24 is fine thread and only could find these bolt in the Lowe's drawers section, they had stainless which is nice because it won't rust but stainless isn't that strong but they had Grade 5 isn't bad, the bin stuff is likely just grade-2 BTW. I might replace it with a grade 8 which is stronger and more corrosive resistant but grade-5 should be fine. I'm using grade-8s to mount the engine.
I don't know how deep the female threads on the shaft go and the Lowe's bolts aren't threaded all the way so I bought a pack of all the sizes from 1" to 3".
The guy in the video I linked also says for attaching the black triangle adapter plates which mount the torque converter safety cover you'll need 5/16-24 for those, and they're on the same side/face as the shaft which likely means everything on that side is 5/16-24 to bolt on a reduction gear (or these adapter plates) etc. take care.