Yes, the A5 and 42 spring will work, and as posted above, you'll need the rifle length 42 and not the carbine length. Of course you'll need to use the A5 length buffer, and which weight will depend on a number of factors such as gas system length, barrel length, suppressed or unsuppressed, etc. Hopefully you're aware of the threatened rules interpretations from the BATFE and other laws regarding AR pistols and braces.