Is this drum safe for UDS build?

I'm sure there will be varying opinions but my opinion is yes it is safe.  As long as you do a good hot burn out of the drum. My drum that I just built was used for aviation grease no liner.  It was clean when I bought it for $25 dollars.  I found 4 pallets at the local recycling center that I got for free along with some scraps of wood beams that a neighbor had from the construction of his new house.  I after I put the last pieces of wood in the drum I had over half a drum of glowing embers.  No oil or contaminants were going to be in the drum after that burn.  In the morning I had 2 inches of ash and a whole lot of nails from the pallets.  I sanded the outside and inside and then cleaned it with rubbing alcohol. 

I think about this.  Just about every smoker that is built weather its $100 or $10,000 dollars starts as processed metal.  It has machining oils and god knows what else on it to keep it from rusting after the steel is made.

As long as you prep it you wont have any issues