I installed a propane burner in my model 60 Lang. I got a cast iron restaurant oven tube burner and drilled a 2 inch or so hole through the box below the wood grate, welded a pipe fitting, and made a wing nut type clamp to hold it in place, then connected the gas valve externally with a large 4 inch washer for a heat shield. If your interested, I can upload a picture of it for you.
It works awesome, I am ready to cook with my hardwood blazing in 15 minutes, no kindling, no newspaper. Also, I can keep the smoker at 175 to 200 degrees without wood if I choose to back off the smoke at the end of the cook or for warming foods, jerky, whatever:-)
Hope this helps,
Steve