With my son enlisting in the Marine Corps, I'm putting together a couple of ARs starting with RGuns engraved USMC lower receivers. Rather than build both in .223/5.56, I'm planning on building one in 9mm.

I've done some research and seems pretty straight forward. I'm leaning towards the Spikes enhanced magwell conversion block because of the magazine selection and still deciding on the upper.

What isn't clear to me is what else is needed. Based on what comes in some of the kits, they also recommend the following:

Ramp bolt/bolt carrier assembly to use AR trigger
Heavyweight buffer to reduce cycle time

Anything else I'm missing?