One never knows what a drum is lined with and most are even if the lining is a thin coat of varnish or nukote or light plastic/BPA.
Drill some air holes 1" X 3 (4). Burn it HOT. Burn it LONG. Wash it scrub it and then Burn it again. Clean it up. Work it over with a knotted wire on angle grinder. Sander. Wire brush. Wash again. So that all the loose metal bits and abrasives go down the drain at the car wash.
Add a grate and charcoal basket. Coat the inside with lard. Fire it up. While the drum seasons play with Temp control. Let it run low for a bit then run it wide open and then slow it down. Hopefully closing everything down will put you out within 15 minutes or so. Find these things out before you start to cook.
Find where 210 -240 is on your air inlet(s). Mine it works out to 2 holes closed with magnets the one air inlet with the 1" ball valve little over 1/3 open. (My air inlets were drilled with a Irwin Uni-bit to 1 3/8")
Second run do it the same but you don't have to run it wide open, put a couple fatties on there, if something goes wrong you're not losing a lot.
Again work the temp control. I found that the Minion method and lighting 8 coals in the Weber lighter and putting in a small dent on the charcoal basket, dropping the coals on, that with the 2 holes uncovered and the gate valve wide it took about 25-35 mins to get the temperature climbing to 205 and I shut the two holes with magnets, at 210 I nudged the ball valve to 1/3 open. Drum went up to 240 and dropped to 230-215 for hours.
If I didn't lift the lid it stayed right there. Lift the lid the temp spikes up once all the way to 340F and I'd have to narrow down the valve so that the temp drops back down then open to 1/3 when it hits 235. I've found that if I close the ball valve for 5 mins then open the lid I don't get that spike or at least not so bad. (sorry my temps are in F(unny) degrees my turkey fryer therm is US temps though it's made in China)
Longest cook I've had so far was 10 hours at -10C and a pork loin roast that was to DIE for. Swear it was like "OH MY GOD. groan grunt smack smack, HANDS off it's mine" But then no pics so it didn't really happen.
Since I made my UDS I'm using it 3 - 5 times a week. I've gained 4 Kilos. Food coming off is so good one just eats more. Plus the fact that I'm cooking 5 Kg roasts and 4Kg butts and brining turkeys and chicken and pork loin and tenderloin and .... I've got to get a good vacuum sealer so I can freeze leftovers rather than FORCING (yeah right) myself to eat them.