I have a left hand Weatherby that I had made into a .500 Jeffrey by Sabi Rifles here in Nelspruit RSA......And I love it to bits!

As to barrel length I'd say go for as short a barrel as you can as it will mean faster target acquisition which is very important in a DG rifle.

FWIW, Sabi Rifles do make left hand rifles at reasonable prices. A client of mine is just having a .458 Lott made to measure on a right handed mauser action and that's costing around R25000/US$4000...........not cheap, but not expensive for a custom made rifle........although it would have cost more had he opted for an upgrade on the wood etc.