What Grit Lapping Compound and which Loctite for Bedding?

[Hansel&Grendel]

I have been sending AR-15 uppers to a specialty shop for lapping for better barrel fitment, at a good price point. I have quite good accuracy by using quality components that equates to happy end users, but I want to do better to include bedding the barrel extension to the upper.

Criterion Barrels has a 4-part AR-15 accurizing video series. I was a bit dismayed to see the CB armorer lap an upper receiver while holding the upper in his left hand and working a lapping tool (Brownells) on a keyless chuck hand drill. I would think that vertical lapping of an upper secured in a vise block along with a chuck-key drill (no lathe at my "shop") would be best to avoid slop. Also, the CB armorer used Loctite 609 to bed the barrel extension to the upper.

So, 3 questions:
1) Is Loctite 609 (the green stuff) suitable or is there a better Loctite formula for bedding the barrel extension to the upper?
2) Instead of outsourcing, what lapping tool is most recommended? (I know that Brownells and Pacific Tool & Gauge have them).
3) Lastly, what grit lapping compound is best for lapping a vertically placed upper receiver when using a lapping tool in a chuck-key drill?

Thanks,
Hans