You should also know that the KMP can be ordered with the original tubular suspension arms and Girling brakes...bringing it much closer to original specifications. The standard (for KMP) upgraded CNC suspension and Willwood brakes will fit the original cars, as the mounting points etc are the same, but are much stronger/stiffer than the originals. They're real pretty, too.
If absolute originality is your wish, an aluminum KMP can be made identical the the originals, a glass car obviously cannot. If a CSX # is what matters to you, then....Of course, you could spend the extra 40K or so, and get an aluminum CSX, but that only makes sense if the CSX # is worth the extra 40K to you. It was not for me.
I love my Kirkham, and the company has been a joy to work with (even though I bought my car from Sal (Powersurge))..