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.
Couple of problems with this I can think of right off the bat.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.