Thanks,
I would like to find one of the old parts books if they show the 'cut in' date for the head. The first production castings would have to precede that by 2-3 months or more.
The HRM road test galaxie (April 65 issue) was claimed to have the 'new' MR equipment. If the car was off the production line and not converted by the engineers I would assume it could have been built around February 1, 1965.