not sure why yesterday's thread got locked, but I'm sure it won't be because of steering racks...
A steering rack has the key advantage over a steering box in that it gives far superior steering feel. This is due to the innards being based on gears rather than recirculating balls and sliding elements. You can instantly tell if a car has a rack or box from the dead feeel about straight-ahead.
A steering system, either rack or box will give much better handling if mounted in front of the axle line than behind it. This is almost entirely due to the arrangement giving an inherent toe-in to the outside wheel in turns, thus giving the driver slightly more turn than he's desired or better handling to put another name on it.
Adding a rack to an Omega B is what I'd call a serious modification, my feeling is that you might as well fit a front-mounted rack to get the best of both worlds.
Actually, getting the geometry right is not too difficult - just make sure that there is NO bump-steer. Ideally, the rack position should be correct to the nearest half millemetre. The wishbone pivot lines are not parallel, so the rack can be mounted fore or aft a fair bit.
I would say rack vs box is a no-brainer, whereas front-or-behind the front axle depends more on what design your sump is.