You are correct.
The Iso-clamp leaf spring holes are larger and require a larger bolt head for that system.
With that said, I did look up the wrong part number for you earlier, Chrysler part # 3643558, from my 77 parts book (for a ’77 F/M body) - my bad.
I just now looked in a ’72 parts book and the (only) non Iso-clamp center spring bolt is 1944361 (which ironically is the same part number that Bill Rolik Enterprises list).
The '72 Iso-clamp center bolt part numbers are 3643558 (standard), 3643579 (police/extreme duty)
The link I provided for did not provide a year range or body style – but most of what they sell is for 60’s and early 70’s A, B, C and E-bodies (before Iso-clamp).
Bill Rolik Enterprises uses the exact fasteners the factory got their fasteners from.
These pictures were taken a few minutes ago, from my 40k mile, pretty much 100% original ’77 wagon. The car has short tires one it (but can’t tell due to the shadows) – which are about 1½” shorter than OE size are (195/60R14 – I think) – so car sits about ¾” lower than it should be.
They came with car and I’m cheap and trying to wear them out before getting the correct size tires reinstalled.
This car does have the optional 5-leaf leaf springs for station wagons (some wagons came with 4-leaf’s).
In-my opinion, the ride height is not bad for a 40 year old car – but springs will be re-arched in next year or two.
The picture does show a “Figure S” shape to the leaf spring – due to weight and sagging, but not due to anything being bent or broke. Just normal sag from age.
A spring shop can get that back to where it needs to be in no time (but most likely I will re-arch them, myself).
a closeup
BudW