Also Mapp or propane can have enough heat if you are able to contain it Once the drops are cut you canslide something over them to hold the heat in. A soft firebrick a can containing vermiculite, or some of the that rockwool insulation, though I haven't tried that myself.

Base your approach on one brick forge designs:

http://www.youtube.com/watch?v=qlKwhIuMdrM