Agreed the T-pipe looks crazy restrictive. If it were me I'd lose it and graft in steel plate around that whole area to make a plenum to the cook chambers. That said, not sure if the firebox is large enough to fuel both chambers. There's a calculator for that(do a search here). And more exhaust is better than less, control the fire at the intake side. JMO
UDS'-55&16, Akorn, Bar-B-Q Kettle, Drum Grill, miniWSM, cobweb-covered gasser. I'm JD.