The info on this at various website is a bit vague, if KR production started late April '68, is that the bucked date for a car or the serialized date? Mine was serialized April 20 and bucked April 30. That that make it one of the first or not?
There are several dates associated with each car. the dates you are giving are Ford dates. If you car was bucked and serialized in April, it would have among the first Cobra Jet cars sent to AO Smith for conversion. Generally speaking most people consider Shelby Number 2263 as the first KR. There was one serial number lower (2008). To make things more confusing, cars were not always numbered in order of the build.