I was surprised at the difference in access between my K1500 axle (11.x rear drums) and my 8-lug K2500 (13" drums.)
So, yeah, you have very little clearance. I don't know of any "special tools" to deal with this aside from normal/ordinary wrenches and generic bleeder-screw tools.
The absolute best way to deal with those bleeder screws, is to
replace the wheel cylinders. New cylinders = new bleeder screws = not seized, no chance of breaking 'em off. And unless you've already examined them, there's a reasonably-good chance the wheel cylinders are leaking already.
'Course, that does leave you with having to unscrew the brake tubes from the cylinder. Or from the brake hose.
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You can kinda expect to need to replace the tubes along the axle, between the brake hose assembly and the wheel cylinders. Common issue. I've replaced those tubes along the axle on both of my GMT400s...and lots of other vehicles.
Don't get me wrong, you should try to free-up the bleeder screws any way you can. But there's a really-good chance that they're gonna break, and that
there's a chain-reaction of failure leading from that. You need to go into this expecting the worst even if you hope for the best.