Robs car is to new.
looking for info about omega 86-93
I posted that link for the benefit of people discussing the Omega as we know it here, even though you asked about the Omega A.
I thought I had acknowledged that on my first reply.
Haynes do a manual for the earlier versions of the Holden Commodore and Calais, think the VN/VP/VR chassis is essentially a Senator A underneath, which itself is the basis for the Omega A platform and was designed from the get go to have a 5.0/5.7 lump in it so adding an LS to one should be a piece of cake.
Be prepared to pay good money for an engine though, as even in the US where they literally grow on trees, they start at $5k for a knackered lump and the manual gearbox is easily the same again.
Basically,,if you're not prepared to put £15k into building it, plus an example rust free enough to be worth doing, then don't bother.