I wouldn't mind a 500 smith in a levergun.
There's a bit of a problem with that. There is a limit to how much pressure certain types of actions can take. You're going to have a real hard time finding a levergun action that can take the pressures that cartridges like 500 S&W Mag and 460 S&W Mag can generate, which are 60,000 and 65,000 psi respectively. Arguably the strongest levergun action is the Winchester model 1892. New manufacture '92s can withstand the punishment of 60,000 psi occasionally, but certainly not a steady diet. Rossi does offer their R92 (based on the Winchester '92 action) in 454 Casull, which has the same SAAMI pressure ratings as 500 S&W. However, most of those people who own those guns guns regularly feed them 45 Colt cartridges to keep the punishment at bay, and I've read reports of guns that get fed a steady diet of 454 experiencing bolt setback when the beating eventually knurls the locking lugs. The problem here is that all these lever action designs lock the bolt to the receiver, whereas virtually all modern actions lock the bolt directly to the barrel.
I've done a fair bit of research on this. I've wanted a lever in 460 S&W Magnum for as long as the cartridge has been out. Just about your only hope is getting yourself a new Browning BLR in 450 Marlin, which has a rotating bolt. Then get yourself a custom barrel for it, and either modify the bolt or get a custom one, and then maybe you won't have to modify the magazine and follower to make it work.
Honestly, just go get a 45-70 and be done with it. It's got more power than the 500, and is commonly available in lever action.