Get some expert advice, mate, and take it from there. A home made steering swap is possible, but you've got lots to learn and will need some professional advice from an engineer. People who don't want to learn the good oil on how to make the original bits on Fords work well should go buy a Honda.
I've studied this one.
What I did:-
I did everything to sort out my old XE, and it steered beautifully when I added
1) the ealier power steering pump, (The XF to XG item was a designed to have a huge sneeze factor at straight ahead because the stock Bishops~Kirby power steering has only 2.6 turns lock to lock, and lots of Commodore drivers found them too waffly).
2) nolathane idler arm,
3) roller top conversion to the power steering box,
4) 4 degrees of castor, new shockies,
5) TRW fully encapsulated top ball joints
and MOST IMPORTANTLY,
6) NO REPCO Pitman arm. The pit man arm must be a perfect Ford spec item. How Repco ever sold such awfull Tiwanese crud as I had on my Falcon, I'll never know. The Vehicle Testing Station rejected a brand new Repco pitman arm, I went to Repco, got 67 bucks back, and then got a new item from Transport Wholesale for 53 bucks, and it was heaps and heaps better!
A run down on what you are doing:-
The problem with Falcon steering isn't that its recirculating ball when its should be more modern rack and pinion. HZ and WB Holdens had the same Bishops~Kirby power and non power steering box, yet pointed beautifully.
The poor old Falcon steering is caused by the castor bars on all XK to XG's, which undergo movement under braking turning, and acceleration. Even the RRS steering doesn't fix everything, but its a quantum leap from the stock set-up.
The later Ford Tristar/TRW power steering rack is a good one, but it is designed to go with the full XH independent fron suspension.
RRS have done all the bumpsteer calculatuons, yet still use stock steering arms and most pickup points.
After helping a mate spend 8 weeks of work on correcting bump steer on his door slammer, I'd say save up for the RRS kit, or get an XH rack, get the Dirt Track Technology book, and start with the stock steering arms, and then shortern the rack. Best rack to use my not be the Ford one. I'd use the Camira or Vectra power steering unit, and make up new mountings and intermediate arms from steel. The RRS set-up is perfect. If your prepared to do your homework, and work with a certificating engineer, then you'll end up doing what RRS did.
I would rather do what Herrod Automotive did to there first XG XR8 conversion in 1994. They just added nolathane idler arms and castor rods. The castor rods won't shear with nolathane, but the top shockie mounts will brake the top mount with the hard plastic, so don't ever use nolathane on shockie tops.
Then, Herrods added the better power steering pump.
The power steering box can be fitted out with a 65 dollar aftermarket roller top ball race conversion. The stock Falcon one is just a plate which soon chops out, and the whole sector can shift, leak, and then some wombat goes and turns the adjusment screw up to fix the steering float, and then the steering box is trashed.
