trepanning

[brendan]

there are a lot of extant Roman era medical instruments - far more than for the medieaval period. They were also made to a much higher standard than the later period stuff due to an economy that allowed specialisation.
In terms of the actual procedure I think that it is described in very clear detail in Roland of Parma's 1290s treatise (which I dont have to hand).
The most important thing is that the incision through the skull does not penetrate the membrane surrounding the brain itself (As far as I remember there are 2).
If you are just drilling a hole then that is one thing, but if you plan on removing a lump of skull you need to drill a few holes and then take a hammer and chisel to the bits in between. I seem to remember a comment to the effect that the patient might show signs of distress at this (As opposed to fixing a tooth ache with a cauterising iron) - so it was VERY painful. And drugs were expensive.
Alcohol consumption would have been limited to that which was suitable to the humours involved (Complicated and I cant remember it so well). Getting the patient drunk wouldnt have been considered good practice by a physician and there was a clear delineation of responsibility between physicians and surgeons.
Oh! Original Roman medical instruments can be bought - a lot have survived. There are a few makers who can do reconstructions.
If you were to reenact it you could use a pigs head - it has all the essential features: Skin; Bone; Brain etc.

Brendan