Huub,
Hmm. Expect everyone is right and there's not enough meat left to re-rifle as you've lost the choke. Maybe, just maybe, you could get a very capable gunsmith to TIG weld new metal at the choke and then rifle that. You are far enough from the breech that pressures should be low enough to permit doing that IF your smith is confident he can get a good weld.
Note also the need to check the serial number and research with H&H to determine whether the 8 bore had the original ratchet rifling of first generation Paradox guns, or whether it moved to the more normal land and grooves of later years. (Not sure anyone does ratchet rifling these days, but just don't know.)
Believe you'd want to get the gun reproofed in London if you did this...
Regards, Tim
