Ah yes, burn barrels. The fun of stirring them up and then digging old half-burned ashes out of them. I finally wised up, made a minor change and now have clean burns and only have to shovel the ashes a couple times a year. How?
Cut -both- ends out of the barrel, prop up about 16" (I use concrete blocks) on a grid of 4 sections of steel posts. Fill, One page newspaper lit under it will have a blowtorch effect going in a few minutes (assuming you have some easily ignitable materian in the bottom of the barrel). Ashes fall through the grate for easy clean up. For hard to start material, I have found nothing better than diesel. I have not other use for it but keep a 1 gal can on hand just for that purpose.
Frank - After you burn it, borrow or rent a backhoe and dig a hole large enough for the old foundation and ashes and bury everything. Then you won't have to worry about nails in your tires or rocks in the way when mowing. This would also be a good place to plant a tree!