Hey Bob
Yep pretty much just lined the bar up, equal distance from cab on both sides and away I went, If you wanted you could take a tape measure to a dealership and measure an St to get the distance.
The existing RX bar wasn't held on with adhesive just the 8 or so bolts, 2 on each leg and about 5 or so across the rear of the tub, all have captive nuts so you just need to undo from the rear side, easy peasy.
I'm new to this forum so don't know how to put photos into this reply but I have uploaded some to the members gallery.
With the rear bar I just had some 6x35mm strips of aluminium plate welded to the existing feet of the bar so that my fixing bolts would be further into the tub, you can't get a nut on the bolt too far back due to the sill being closed. I did fit the rear bar at a slight angle to get a bit more distance between it and the front bar for load carrying and I will eventually fit a pull out awning, Having that slight angle meant that the feet of the bar sat flat onto the tub rail.
As you can see I have then fitted Rhino Bars that I kept from my Pootrol above the sports bars.
Hope this all helps
Good luck