Here is my opinion....for the money spent on one of these (and they are probably worth it), Why not just get a suitable Marlin or Winchester, rebarrel and rechamber for the 500? The cost of the Marlin or Winny plus the new barrel and chambering....and, an action rework if need be for the new cartridge would most likely not cost as much as the Big Horn........and, at least you would not have your 600.00 deposit tied up, and wait indefinately to get the rifle.
Agree with Flat Top. I think a good candidate would be a Rossi M92 in 454 Casull. The M92 is a stronger action. Not sure if it could be done but that is a good suggestion.
Couple of problems with this I can think of right off the bat.
1st - The 500 S&W's OAL is much too long to fit in a '92's action.
2nd - While strong, I don't think that the '92 can take the increased bolt thrust of a 60,000psi .50 cal round.
The 65,000psi 454 Casull has a bolt thrust of 11,762psi while the 60,000psi 500 S&W has a bolt thrust of 13,038psi.
For comparison, the 35,000psi 357mag's is 3,948psi while the 36,000psi 44mag's is 5,905psi.