O.K. This may be of no help at All.
About 30 Yrs ago I started to Convert a 59 Custom Royal to Front Discs.
I Found that the Disc off a 69 Plymouth / Dodge Phoenix had the same bearing Spacing & Sizes as the Drum Brake Spindle on the 59 & Slid straight on.
I Figured after that it was only a Matter of making a Caliper Mount.
However Halfway through this Exercise I Stumbled across a 73 Monaco.
(Long Story, I'll try to Shorten it), I used to have a Job that Required me to Visit all the Wrecking Yards in my State.
One Day I Visited a Yard I was very Friendly with. Parked out the Front was an Extremely Battered 73 Monaco.
Upon asking the Owner what the Story was he explained to me that this was his Friends Porsche.
Apparently his Friend had gone to the States for a Visit & while he was there had found a Very Nice Little Porsche at the Right Price.
He Purchased the Vehicle went to a Shipping Agent & arranged for it to be shipped to Aust.
When the Container arrived & was opened what they found was this beaten up Monaco.
The Fella never saw his Porsche but I bought the Monaco.
Anyway, It was a 400 C.I. 727 with Boosted Disc Brakes.
The 73 Monaco had changed back to the 59 Style Ball joint Set up. so I switched to the Idea of using the Monaco Assemblies.
Now from Memory the Monaco Stubs were Slightly Taller than the Custom Royals. So there may have been a Problem with the Steering Geometry.
(Was looking at the Idea of Machining the Top & Bottom of the Stub).
Also with the Larger Ball Joints on the Monaco I had to get a Machine Shop to Turn Up some Tapered Sleeves for the 59 Ball Joints.
Unfortunately During All this I was Retrenched, was out of work for 8 Months, ( Don't get Old Nobody wants to Hire You.) And Eventually had to sell the Car.
The Fella that Bought it Still hasn't Finished it, so I Can't tell you what the Eventual Result was regards the Steering Specs.
Sorry for what may be nothing more than a Long & Boring Rant. Hope I haven't Bored you and that this Info may be Helpful in some way or other.
Regards Tony.M
P.S.
My Personal Opinion is to Make up some Caliper Mounts with the 69 Discs.
That way you are Not Altering the Original Steering Geometry in Any Way.