I've never seen an Original '65 model year 200 cid car with a Blue block... So far I've never seen any original examples....I think that it's mostly a load of "bunk".
Sure, Ford Corporate Blue 200 cid engines were produced in Late 1965, but they were designated for 1966 Model year cars ONLY. I've been doing this 30+ years and I have yet to see an unrestored Original 1965 Model 200 cid six banger with a legit "blue" block and blue painted accessories. If there were any of these "Changeover" late '65's models with Original Blue '65 200 blocks... I have yet to see one.
My own '65 Convertible 200 had it's own block painted Ford Corporate Blue by a Previous Owner which is obviously incorrect. It clearly had signs of the Original Factory Black paint underneath the Blue paint.
In other words, Paint your '65 200 cid block Black with the Red Orange Valve Cover to be "Correct" for your '65 Model year car.
When the 1966 Model Year was introduced in Late August '65?...Ford immediately went to Ford Corporate Blue for all of their engines...but that was ONLY after the 1965 Model year run was completed. I have never seen any other evidence to prove otherwise...If there is any, It would be great to see.. I welcome it.
Melbourne, FL (Formerly from Long Island, NY!)
1965 Mustang Convertible 200cid I6, 3spd Manual
1966 Mustang Sprint 200 Registry Owner/Moderator
1966 Mustang Sprint 200 Convertible 200cid I6, C4 Auto
2007 Mustang V6 Convertible w/ Pony Package