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I have a 1957 GMC 1 Ton that I thought had the original 347 the engine has the front motor mount not side. But block numbers are 533087 that tells me it is a 1959 389cdi but the bore is not 4.0625 it is only 3.820 thanks for the help.

There should be a stamped serial number on the right side of the block near the oil pan if it came off a truck. The first three digits are engine size. I don't know if car engines had this or not.

Well if it is indeed a 59 GMC engine, it would be bored .040 over. The 59 Pontiac motor, and the 59 GMC motor had 3 inch main bearings. The 347 and the 370, as well as the first series of 336 motors used smaller main bearings.

Why am I rambling about the bearing size? You can get a stroker crankshaft for the 59 and on Pontiac motors to increase the stroke by 1/2 inch. I have a 59 pontiac 389 in my 59 gmc that has been bored .030 over (4.0925)and stroked to come up with 447 inches.

It does have 3" mains and 2 1/4" rods. I found the numbers stamped by the oil pan there were two of them one on top of the other first line was 3364 the second was 3930 so would it be a 336?

It is indeed a 336, based off the 59 pontiac 389. However if you need a head gasket, the Pontiac 347 or 370 head gasket will match up a little bit better with the bore.

Edit: The 370 has the same bore as the 389. The stroke makes up the difference in displacement.