My advice, if you plan to keep the car a very long time (I've had my Alpine for almost 30 years now), is to buy a new set of wheel cylinders... then immediately send them off to White Post Restorations (or whoever) to bore them out and slip in a bronze liner... then have the pistons blued to inhibit corrosion (a good gun shop can do that for you), and put it all back together, using silver antisieze lubricant on the threads of the bleed and tubing nuts, on the tubing inside the tubing nut, and on the bolts attaching the cylinder to the backplate. You'll never worry about your wheel cylinders ever again.
If you really want to keep the ones you have, then, if you can get off the brake tubing nut, take off the cylinder and use a drill press and a proper drill press vise to drill out the bleed screw - don't even attempt this with a hand-held drill. If you can't get the tubing nut off, then cut the tubing, because that connection is toast no matter what happens - replace the tube with both nuts.
I know a lot of folks like to use left-handed drills, but the problem I've found with those it that they aren't readily available in a lot of sizes, so you have to make compromises - drilling a not large enough hole or too big a hole. Instead, I use right-handed number drills (not fractional) so that I can carefully go up a little bit at a time until I'm left with just a thin spiral of threads which I can then carefully pick out with a dental pick. The nice thing about a bleed screw is at least you already have a pre-drilled hole to center things up.
Having said, that, I still recommend the bronze sleeves whether you use your existing cylinders or new ones. They are *wonderful* and will indefinitely preserve the life of your brakes.
A couple of final notes: On tubing nuts, *always* use a proper flare-nut wrench, never an open-end wrench - this prevents crushing and/or rounding off the nut, as well as makes it easier to apply the proper force without slipping off and busting a knuckle. Also, when unscrewing any really stuck nut or screw, I find that *tightening* it just a bit, before you back it off, actually can break free things that ordinarily would not come loose.
