This fresh engine is in our '69 X33D80 VIN#124379N658489. Heads are 186's dated Dec 1 '68 and Dec 2 '68.
Will consider swap out of block and heads for late May - early June (prior to 6/16 assembly) block and heads in similar condition.
N658489 was final-assembled on or about June 18th. Z/28s built in that VIN range have engines built May 15-May 29. 8 dates are known; no one looked at dates and engines were not issued first-in-first out.