Rocky Porkchops

Team, Woo hoo! My first post! So, my neighbor bought a Bear Creek Arsenal (BCA) complete upper (side-charger) w/ 10.5” barrel in .22 WMR. BCA doesn’t offer a complete AR pistol with that barrel length in .22 WMR, so she has a few questions before she buys a complete multi-cal lower for it: 1. What size/weight buffer? 2. Buffer spring particulars? 3. Receiver extension length? 4. Other pertinent info to give her an optimum build (limiter pad, etc.)? Thanks! I will pass along to her any and all helpful information or advice. See: https://www.bearcreekarsenal.com/22-magnum-10-5-parkerized-heavy-barrel-1-16-twist-10-mlok-rail-sch-nrail-branded-upper.html