O.K.
Long & Possibly Boring Rant to Follow.
Many Years Ago I had a 1959 Dodge Custom Royale.
Wanted to Convert to 69 Plymouth Fury P/Steer.
Had a Fella with a 59 Plymouth Fury who Also wanted similar.
He was a Truck Chassis Modifier / Designer.
The Chassis in My 59 was 80 Cm (Approx 31.5 Inches) between the Rails, the Sub Frame in the 69 was 81 Cm between the Rails. (Approx 31.75 ? Inches)
Obviously Very Close.
I Supplied a Complete Set of P/Steer in Exchange for Him Doing My Chassis when He had Finished his Own.
He managed to Do the Conversion & was Very Happy with the Result.
Sadly He Passed away before he could Convert My Car.
But as I remember it was a Matter of Mainly Notching the Chassis to Accept the Later Model Box. I Assume Copying from the 69 Sub Frame Design.
(Please Remember we are Talking R.H.D., Compared to L.H.D., The P/S Box Sits In an Entirely Different Location on the Chassis Rail, Not Just Mirror Imaged.)
Please take Note. Modifying a Chassis is Definitely NOT a Job for the Average Competent Welder, He has to Know & be Experienced in Chassis Welding / Modifying.
Having said that, I do Feel that it is Not That Big a Job if You Know What Your are Doing. Just Not a Job for a Backyard Welder. Even an Experienced One.
In Regard to Rack & Pinion, Although I know of a Number of "A" Body Conversions that are "Apparently" Successful, (Mainly for 383 / 440 BB Conversions)
I also know of a Couple of "C" Body Fellas who Converted to Power R&P and were Really NOT Satisfied with the Result. (Super Wide Turning Circle, Heavy Handling Etc.)
Now I Need to Put a Qualifier on My Remarks.
This was 25 Years Ago & here in OZ. We Just Did / Do Not have the Variety of Resources or Technology that is Available in the States.
(You Fellas have a Far Wider Range of Vehicles to Choose From)
I will leave it up to your Fellow Americans to Best Advise You.
Just Hoping these Comments May Prove Helpful / Informative!
Kind Regards. Tony.M