I didn't realise when I started to read this thread that the tastes and opinions of myself and Kiichi are now so close that we're merging into one person! :D I'll need to say something that provides a bit of distance between us.
I've heard nothing but good things about the Rebel Yell in a Les Paul but for me, it's too much of a Rock pickup for what you want and it seems to me that the hotter you go, the further you move away from the classic Gibson Les Paul voicing that the OP is after. Providing the guitar isn't hugely dark and you do want some power in the pickup, putting a Crawler in the bridge is the obvious solution. It's hot and has some real growl to it but unlike other pups in the contemporary section, it's not massively tight and retains more of the PAF DNA than the others. Of all the pickups I've tried, the Crawler gives you the largest operating window, though I believe the Mule and Abraxas are also very good at that. You can play Blues with it, Blues Rock, Classic Rock and it will even take you into some early Metal styles. There's a real richness to its tone that is simply sublime. If you weren't going to get the Crawler in the bridge, I'd only really be looking at the Abraxas or Mule, though I find Kiici's suggestion of a Black Dog to be a really interesting one. If you want vintage tone in the neck, I'd just use a Mule regardless of which of these bridge pickups you select.
So that I don't distance myself too much from my good friend Kiichi, I'm also going to say that whatever pickups you choose, remember to spend time playing around with the height of the pickup as Bare Knuckles are incredibly sensitive to height adjustment. You can also do a great deal to tweak your tone by lowering the height of the pickup but raising the height of the pole pieces as this can do wonders in adding note definition and losing a bit of bass. 8)