It was common for Ford FE engines to have "352" cast into the block. It doesn't mean it is a 352. See
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What color is the engine painted? Back then the different size engines were painted different colors. A 1964 390 should have a black block with gold valve covers. Here is a list of Ford engine colors I borrowed off the internet:
YEAR/CID/ ENGINE BLOCK AND CYLINDER HEADS COLOR/AIR CLEANER COLOR/VALVE COVERS COLOR
1959 223 Black Red Red
1959 292 Black Red Red
1959 332 Black Green Green
1959 352 Black Blue
* Blue
1960 223 Black Red Red
1960 292 Black Red Red
1960 352 Black Blue Blue
1960 352 HP Black Gold open-element Gold
1961 223 Black Red Red
1961 292 Black Red Red
1961 352 Black Blue Blue
1961 390 Black Silver Silver
1961 390 HP Black Gold Gold
1961 390 HP-6V Black Oval aluminum Gold
1962 221 Black Yellow Yellow (not positive on this one)
1962 223 Black Red Red
1963 260 Black Light Blue Light Blue
1962 292 Black Red Red
1962 352 Black Blue Blue
1962 390 Black Silver Silver
1962 406-4V Black Gold open-element Gold
1962 406-6V Black Oval aluminum Gold
1962 221 Black Yellow Yellow (not positive on this one)
1963 223 Black Red Red
1963 289 Black White White
1963 352 Black Blue Blue
1963 390 Black Silver Silver
1963 406-4V Black Gold open-element Gold
1963 406-6V Black Oval aluminum Gold
1963 427-4V Black Chrome open-element Chrome "baldies"
1963 427-8V Black Oval aluminum Chrome "baldies"
1964 223 Black Red Red
1964 260 Black Light Blue Light Blue
1964 289 Black Red Red
1964 289-4V (not HP) Black Gold Gold
1964 289 HP Black Chrome open element Chrome
1964 352 Black Blue Blue
1964 390 Black Gold Gold
1964 427-4V Black Chrome open-element Chrome "baldies"
1964 427-8V Black Oval aluminum Chrome "baldies"
1965 240 Black Red Red
1965 289 Black White White
1965 289-4V (not HP) Black Gold Gold
1965 289 HP Black Chrome open element Chrome
1965 352 Black Gold Gold
1965 390 Black Gold Gold
1965 427-8V Black Oval aluminum Chrome "pentroof"
1965 427 SOHC-4V Black Chrome open-element Cast aluminum
1965 427 SOHC-8V Black Oval aluminum Cast aluminum
1966 240 Blue** Blue Blue
1966 289 Blue Blue Blue
1966 352 Blue Blue Blue
1966 390 Blue Blue Blue
1966 427-4V Blue Chrome open-element Chrome "pentroof"
1966 427-8V Blue Oval aluminum Chrome "pentroof"
1966 427 SOHC-4V Blue Chrome open-element Cast aluminum
1966 427 SOHC-8V Blue Oval aluminum Cast aluminum
1966 428 Blue Blue Blue
1967 240 Blue Blue Blue "PBF"***
1967 289 Blue Blue Blue "PBF"
1967 390 Blue Blue Blue "PBF"
1967 427-4V Blue Blue Tall Chrome "PBF"
1967 427-8V Blue Blue Tall Chrome "PBF"
1967 427 SOHC-4V Blue Chrome open-element Cast aluminum
1967 427 SOHC-8V Blue Oval aluminum Cast aluminum
1967 428 Blue Blue Blue "PBF"
1968 240 Blue Blue Blue "PBF"
1968 302 Blue Blue Blue "PBF"
1968 390 Blue Blue Blue "PBF"
1968 427 Blue Blue w/chrome lid Tall Chrome "PBF"
1968 428 Blue Blue Blue "PBF"
1969 240 Blue
**** Blue Blue "PBF"
1969 302 Blue Blue Blue "PBF"
1969 351 Blue Blue Blue "PBF"
1969 390 Blue Blue Blue "PBF"
1969 429 Blue Blue Blue "PBF"
1970 250 Blue Blue Blue "PBF"
1970 302 Blue Blue Blue "PBF"
1970 351 Blue Blue Blue "PBF"
1970 390 Blue Blue Blue "PBF"
1970 429 Blue Blue Blue "PBF"
1971 302 Blue Blue Blue "PBF"
1971 351 Blue Blue Blue "PBF"
1971 390 Blue Blue Blue "PBF"
1971 400 Blue Blue Blue "PBF"
1971 429 Blue Blue Blue "PBF"
- The blue used on these engines is very similar to the lighter blue used on the late-'60s Ford engines.
** The blue used on 1966-1968 Ford engines is a darker blue than used on earlier Ford 352 valve covers. The correct color is TRW #630224 or Eastwood's "dark Ford blue."
***"PBF" indicates "Power by Ford"
**** 1969-1974 Ford engines were a lighter blue than 1966-1968. The color is similar to the early 352 valve covers.