I’m trying to clear a house lot that had a thick area of vines, smilax, and briars. The job is to large for me to do by hand. Are there any machines the could do the Job? I dont think a garden tiller will be enough. It is about 8’ Out from a fence that cannot be moved.
A hedge trimmer and a chain saw will get through everything above ground, unless you have large trees which need to be felled by professionals for safety reasons anyway.
If you don't have large rocks below ground, a stump grinder will chew through everything down to a depth of a foot, not just tree stumps. "Small" stones (say 2 inch diameter) are not a problem, but be prepared for the machine to shoot them at anything breakable nearby - including people!
Note, using a stump grinder is hard work - it doesn't propel itself through the ground, you have to do that yourself. If the job is going to take several hours, it may be better to hire one from a company that will also do the work, rather than attempting to do it yourself.
All those tools will work to within an few inches of a fence (or even a stone wall) if you have enough experience to control them - 8 feet is no problem at all.
Of course this only solves the problem of ground clearance. Killing the unwanted vegetation is another question.