the EIN / Engine Identification Number is just a truncated form of the VIN / Vehicle Identification Number that the engine came from. unfortunately, that means that there's not a whole lot of information that can be discerned from the EIN beyond year and the plant that the car came from unless you've got a prefix of 7, 8 or 9 on the Sequential Production # portion of the EIN.
6 H 226988
6 == 1966
H == Flint Michigan
226988 == sequential production number, will match last six of VIN
6 D 10754
6 == 1966
D == Doraville, Georgia
10754 ==sequential production number, should be six digits
an SPN that began with "9" would belong to a Riviera, but that's not going to happen with a small block engine anyways. for 1966, all Rivs would have had a 401ci or 425ci Nailhead.
casting #s are very sketchy for these early engines so if you could have a look at the "Small Block Casting #" thread and help us out we'd appreciate it.
the two letter Engine Code stamping will give you slightly more information, but not much:
your engines should be stamped
MA == 2 barrel carb
MB == 4 barrel carb and intake
MX == low compression export engine
ML would denote a 300ci 2 barrel.
"M" is obviously the year code for the Engine Code stamping. 1965s are all "L" coded and 1967s are all "N" coded.
how did you come to wind up with TWO 340ci engines in SWEDEN? those are pretty rare ( 1966 and 1967 only ) even here in the States.
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