Barrel compatibility?

I have a stag 2HL (lefty) 16" Carbine upper.

I’m wanting to build a SPR upper (18" 1/7 Mid) and wondering if I can just swap out the barrel?
This would save $$ over buying a complete new upper.

Someone mentioned making sure the new barrel has an “Ambi Extension”…

Thoughts?

You do need a Stag Ambi barrel extension.

Thanks Todd…