The BB is a heavier weight than the H2. The H2 is 4.7OZ and the BB is 5.7oz.
For the 300 blackout, i would recommend our SMB-C if shooting unsupressed in a a rifle. SRS if shooting suppressed on a pistol. Feel free to reach out directly to Armaspec for more recommendations.
We would recommend that you run the SRS-BB on this build.
This would depend on the barrel length and suppressor type. For a Shorter barrel with a normal non-flow through can a SRS-H3 would work great. For the same configuration with a flow through can I would recommend a SRS-H unit. For a long barrel with non-flow through can we would recommend a SRS-H2 and a SRS-C with a flow through can. Also some barrels have a smaller port designed for suppressors and these would use a SRS-C instead.
We would recommend that you run a SRS-C and you also need to use the A1/A2 spacer that Armaspec makes to run it in that buffer tube.
There is no way to convert the H2 into a AR10 as they use different weight, black bumper, and spring.
The SRS can not be ran out of the box with the Law Tactical Folding Stock Adapter. I would recommend reaching out directly to Armaspec for recommendation.