I would just make those four 3/4" holes into four 1" holes.
I have four 1" holes all with elbows, two have 3" pipes with caps and two have 24" pipes with elbows at the top for the magnet air controls.
No problem getting to 275*. Once it hits 190 I cap the two short ones and control the final temp with the magnets.
Drumhead - UDS x 2 & UDG
Keep on Smokin'
KC native missin' KC
IMBAS Certified MOINK Baller 2009
I also support PETA - People Eating Tasty Animals