Can you provide pictures???
Many casting numbers can be found in the Chevy Master Parts Books, using
GM Partswiki searchable database. I just did a quick check using that casting number and came up with no matches unfortunately.
Casting numbers are notoriously known for being difficult to read/easy to misidentify, so picture are a big help getting past that issue. Also of importance is the transmission has many different casting numbers. Main case, tail shaft housing, side cover, etc. The most important one to start with will be the one on the main case.
Please post some pictures,if you can and we offer more help.
