I'm with FastJake here. The OP's goals of hidden cables and 8 (or7) speed shifting can be achieved with Modern Sora (ST-R3030-L and ST-R3000-R) shifters and a vintage Dura Ace RD-74XX rear derailleur. No alternate cable routings required.
I'm doing a similar thing for my son's race bike at the moment.
Cheers,
Cameron