Found this , thought I was interesting
SDR
PREFIXS
C - The third series of AC Ace variations.
S - SheIby.
X - Export (left-hand drive).
B - To be sold In Britain (right-hand drive).
AK - Autokraft
BUILT BY AC IN ENGLAND
CSX2000 series: - MK.I and MK.II Cobras (1962-65) sold by Shelby In the United States. Leaf spring suspension. 260 or 289-inch engines. Left-hand drive.
CSX3000 series: - MK.III Cobras (1965-67) sold by Shelby In the United States. Coilspring suspension. 427 or 428 cu inch engines. Left-hand drive.
COB6000 series: - All Cobras (MK.l. II and III) sold in England by AC (1962-1969). MK.III COB Cobras used 289-cu inch engines instead of big-blocks. Right-hand drive.
COX6000 series:- Same as above but sold in Europe or the United States (but not by Shelby). Left-hand drive.
CSX5000 series: - Intended to be used for a special run of Ghia bodied Cobras (1966). Only two made.
AK000 series: - Cobras built by AC and Autokraft since 1982. MK.IV model uses 302 Ford. various engines optional. Most based on MK.III Cobra. but a few MK.II models buIlt as well.
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BUILT BY SHELBY IN THE US
CSX3000 series:- The Continuation Cobras sold by Shelby the past few years have unused numbers left over from orIgInaI427 Cobra productIon.
CSX4000 series:- The new Shelby component car. MK III chassIs. fIberglass body.
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OTHERS
CSX-R4000 series: - Cobra replicas whose manufacturers contribute to Shelby Heart Fund or are otherwise endorsed by Shelby. RAM Automotive in England is the only one at this time
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