[nuch_ss396]

Look for "HI-PERF PASS" cast into the block down by the oil
filter boss ( left rear of block ) or under the timing cover
area. The use of these "signifiers" was not constant throughout
the years though. I have also heard that the "T" was for Tonawanda,
but never "TRUCK". Truck blocks have tall decks and a '512
doesn't. Most likely, the "T" is for Tonawanda and the "P"
is for passenger.

BTW, what are the casting dates of the blocks you have?

Steve