So, here's the short story on your block casting by the casting number;
"14093638 - 1987-1995 350 Car & Truck 2 & 4-bolt Passenger stick 1-piece seal"
Not sure what you reference to "GM 5.0LG" is, but the engine is clearly a 350 cid, 5.7 Liter.
The 5 Liter GM engines were 302, or 305 cid, usually through the '80's and loaded down with pollution control stuff! :roll:
Sorry to jump in ... new to this forum and have a similar question.
I purchased a 1981 firebird that had its engine swapped from its original 6 cylinder to an 8 cylinder, but I have no information on the specs.
I'd love some help deciphering the numbers I have found on the block thus far: