See what a little kindling can do, Lew? Passion is an understatement.
I'll sidestep the sheep dip; I'm from NY and we are not familar with that condiment.
Maybe some of this can help:
(footnote credit for some of this to SpecialK)
I believe that the Kirkham-based cars that become CSX4000's are based on a body and frame-only assembly that is OEM'd from KMP. Suspension and running gear are all SAI parts.
The majority of suspension and chassis parts that are used on both the CSX4000 and the KMP427 are reasonably interchangeable with the corresponding CSX3000 part.
The 4000 cars have adjustable front upper control arms that allow castor and camber changes. 3000's only allowed for camber adjustments.
4000 cars have aluminum Salisbury style differentials, 3000's have cast iron. KMPs can have Jag or Salisbury type diff.
Baer brakes are used on the 4000's, with Girlings optional. KMP has either Wilwood or Girling-style.
The common frame is pretty much dead-nuts to the original, with thicker frame rails...they have .120 wall D.O.M. framerails, 3000 cars have .095.
The SAI-made frames have some superior tubing choices and welds that are unparalleled in the Western hemisphere.
Since, usually, either an SAI or KMP is fit-and-finished by the owner or builder...the degree of authenticty is up to whatever you would like to do. Vintage or period parts fit just as well as any modern pieces supplied by either manufacturer.
As a daily driver, I think the suspension differences of the two are moot.
Questions?
A few facts
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