our friend from oregon makes a good point: with a large amount of coals like that you might get some direct cooking on the bottom of the meat. so if the bottom of that pork looked like it was cooked from below then you will need to make an adjustment to your process.
the easy thing would be to simply make a shield that can lay on top of your fire basket and reduce the direct heating. that may be all you need. another approach would be to use some type of pan that would be large enough to catch the drips from the meat and serve as a heat deflector as well. a large round kettle from the boot sale might work. some people fill there drip pan with water also.
I find that the amount of charcoal is not so important to the burn rate as the amount of air coming in. so if you get the right temps with that large basket and with the air inlet that you currently have then you are on the right track. there are many different ways to manage your fire, oregon blues has his, I have mine. Now you need to find yours. since you do not have a good way to add coals without opening everything up, and thereby loosing cooking temps, you should investigate "the minion method" which is used by many with weber smokey mountain cookers. this is a very effective way to cook in the right setting and I think it may be what you are looking for with that drum.
how well did you hold temp and what temp did you cook that pork at? it looks pretty good to me, so you are well on your way.
when cooking pork I try for a temp range of 225-250 F and a 10 pound pork butt will take me 10-11 hours at that temp. I pull it off when the internal temp of the meat hits 190-195 F.