Its a 1968 two bolt main 327. From this website, Small Block Casting Numbers

 

Its a 1968 two bolt main 327. From this website, Small Block Casting Numbers

2 bolt mean. I needs help with that T12 CONV 1

 

18Z 157246 = Chevrolet, 1968, Fremont Assembly plant, 157246 = Sequence number. This string is also known as the CONVIN. It will be stamped in all locations containing the ConVin AKA partial VIN.

T05I5EC = Tonawanda Engine Plant, May, 15, EC= L30 327 4BBL, 275HP W/ POWERGLIDE TRANS

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GM 3914660 Block Casting number = 2 bolt 1968 327

T12 = You got me, that's not the block casting date. Might be the mold number.
CONV 1 = ?

 

Thank you so much man your fast. I still can't find those numbers either T12. Thank you at least i got a good start with the block 275. I think with a turned motor and crank, re did the heads, new cam, new intake, new timing chain, new 4 bqrrel AVS2, new 700r trans, heads and mufflers, with new almost everything i believe if i time it right i should push 350-370. I hope. Too many new parts all match so its a smooth machine monster. Whatcha think?

 

I've seen several Tx or xT castings as well as CONV x and agree they're most likely mold identification like those on a rear end housing. A casting date would be more like 2 25 8 for a Feb 25, 1968 casting date.