water in the oil

Looks like you have pea soup. The water pump bolts do need sealant, but even without you’d only get a very light amount into the block from seepage. Could be the intake gaskets or the head gaskets. What do you mean by high profeomace gaskets?

Personally if it is a 340 block, I’d pull the motor and do a refresh. Pea soup and bearings don’t get along and you’ll have more problems down the road. From bearing failure to whipping the cam out... just sayin...

As for the date code and block size, it is cast into the side of the block and stamped into the front side of #1 cylinder near the deck. Vin is on the machined pan on the passenger side of the block right above the oil pan lip midway of block.