If you bought larger bolts to fit the AP2 diff, they'll be too big to fit through the AP1 driveshaft holes.
If you re-used your AP1 bolts the AP2 diff bolt holes are too big.

A new flange nut is not the issue, nor Locktite The flange nut must be tightened to a point whereby the diff input shaft has a specific, and slight, resistance to turning. You measure this turning resistance with a torque guage that has a very precise/fine tolerance.
It's not really possible to just tighten the flange nut without testing the turning resistance because it's the resistance that determines the force with which the inner diff gears mesh with each other.

I'm no diff expert however I'm pretty sure this is the issue at hand.

 

I don't think he seems to be following what we're trying to explain.

You don't NEED to replace the collar but you WILL have to replace it if you **** up the torquing process and you don't have the correct rotation torque after swapping flanges. Which then you will have to open up the ENTIRE diff to replace it and set all the gears after installation. But I already said this.

EDIT: And if you **** up the torquing process after installing new crush collar, guess what? You have to open up the diff again and do the entire process all over again with a new collar.

Like I already said, save yourself the headache and get an AP2 driveshaft along with an AP2 transmission flange. Simple swap over.

 

Ah, okay. I get it now. Nobody ever said that I didn't NEED to change out the crush collar. My plan this whole time is to have a driveshaft/drivetrain shop change out the flange, and they will obviously have the correct tools and knowledge to do it correctly.



I understand the bolts don't match up.. but what about bolts from a specialty/hardware store? That seems like the easiest, cheapest and most practical option?

 

It's a car not a bicycle. Spend the money and do it right.

 

Doesn't matter where you get the bolts, the point is the ap1/ap2 are two different sizes. You cant mix them.