Ant

Hmm......... interesting. Guess you wont really know until you pull the sump. Casting date is pretty simple. 4 is the year, A is the month, 23 is the day. So your block was cast in the foundry on Jan 23 1974. Even though your engine block casting number is 1972. (D2) thats the moulds they used, same for several years until they wore out, or changed engines. 
You may find that you just have a 351 2V, but, they used the same block for the Boss, Cobra Jet, etc.. but modified them later for screw in studs, different heads, 4 bolt main caps.
 
Carb, cam, extractors and ignition.
 
Change diff ratio for what you want the Effie to do, Tow truck, quick off the line, fuel economy....

Hi mate, you're correct. JG31 is a Falcon 500 wagon. To check the displacement without removing the sump or heads, pull a spark plug, stick a drinking straw in the hole and slowly wind the engine over by hand/socket. Measure how far up and down the straw goes. 302 had a 3 inch stroke, 351 had a 3 1/2 inch stroke. Heads can be tricky, as to whether they are 302/351 closed chamber or open chamber. I have heard MANY stories/tales of peeps saying they are right, they have a factory blah,blah with special order blah,blah....... obviously the best way is removing the heads and have a look. Depends on what you want to find out. If it's running sweet and not blowing smoke, don't care and drive it like ya stole it.!  
 
D4 engine casting is roughly 1974.  But the numbers dont make sense to my tiny brain. Normally something like a D4DE - 6015.
C is 1960's, D is 1970's, then the actual year,  (so 1974 )D for Falcon, then it usually has an E for Engine. 6015 is block.
 
Hope this gets you started.

G'day Sparky Dave and everyone who might help. Hope its ok to start a new thread as well as post it here as I'm not sure if anyone will see it as this thread is older. Sorry if this is long winded. After typing all this out with one finger it seems so.  I just joined this forum to see if you might be able to help. The info you posted on this thread is the most accurate I've found.   I have recently  purchased a Ford F100 1977 long wheel base 4x4 automatic floor shift with a (351 Cleveland maybe).  From what is posted here I believe I have verified I have a 1977 ford f100 4x4.  But that's where I don't know the rest.  The vin is AL4KTR50448K  Model code is 64727  Engine code is Y (I need help here it looks like Y is a 302) Transmission code is L (which is 4 speed manual and I have auto). SDIO code is 929334   Engine number in the truck is JG31RP61522K (which it seems comes up as from a 1975 ford falcon station wagon) but I don't know how to check the engine capacity or other engine specs, heads if I am right about that?  Looking at the block casting it's D43DCA. I don't know what this means but its the square Cleveland block with no numbers on the heads.  When I purchased the guy said he has owned it for 15 years and bought it from a dealer who said the engine had been rebuilt with high compression heads by the previous unknown owner and its a 351 Cleveland. I get between 175 psi to185 psi compression test.  So now I'm on the learning curb trying to figure out the codes to see what I've actually got. which I'm gathering at this point its a 1977 Ford f100 4x4 long wheel base and the engine and transmission have been changed or its the original engine and transmission. Its either a 302 or a 351. The heads look like 351 but what was factory for this vehicle is what I'm after are engine specs for the engine I have and where it originally came from.  Cheers and hope you guys might be able to help out.