First of course the June date is likely the date from the door tag and not likely the real date but, lacking the VIN it does give us a general idea of when the car might have been built. With that said common belief as stated would be that all of the late 65 V8's were painted with a black engine with gold (except Hipo) valve covers.
I looked through my pictures and honestly have to entertain the slight possibility that San Jose may have receive a limited number of engine painted blue as a possible test of something. We know San Jose was used as a test bed for some other changes related to engines. Would suggest that the possibility would be difficult to convince everyone of especially since this is a very long term and strongly held belief (black engine assembly)
Of course there may be a reason for this group of unusual findings but I found it interesting that the VINs were clumped in an approx 10,000 unit spread at one plant. Much easier to not go down the rabbit hole but we're here to share and discuss if there are discoveries. Would be interested in the owners cars' VIN to see if it fits the pattern.
Yes I can hear it now ... its possibly a can of worms
Believe the document Bob was referring to might be in this thread
http://www.concoursmustang.com/forum/index.php?topic=5011.msg27955#msg27955