I think drilling an 18" barrel (about 14" hole as I recall) will be virtually impossible on a short machine like that. You should be able to do the outside but to use it for drilling, you'll have to make a bed extension that lets you move the tailstock off the end far enough to get the drills in place. That is not impossible.
I did such a thing for my 17x54 when I had to turn 6' poles for a project. It was easier in my case as the tailstock could be bolted in one position rather than having to slide down the bed, but you don't need to make the extension from cast iron since it won't be used very much. You do need to get the V way on the extension accurately aligned with the one on the lathe bed or you will get an oversize hole from the misaligned drill. Be sure to supply a foot under the extension so you aren't cantilevering the weight of the tailstock from the bed. And provide a way to tie the extension to the bed so it isn't forced away by the drilling force.
i was thinging of taking off my tailstock, and moving the carrage down to the end,
making a mounting for the 4X18 round , removing the toolpost,
and mounting it,
putting the drill bits in the 3-jaw, move into the drill, back out,
probably only drill a few inches switch bitts, to a larger size, making room for extensions,
back and fourth, for ever,
then move the round forward, in the mounting, when needed,
also having a weight in front of the carrage to balance it,
im working on having someone else do it for me, if its a fair price,
just the drill bitts would cost me an arm and a leg and im shure the poor little lathe would take a beating,
johnp