Hey, thanks for the replies. Ok, so I know I have a Z24(S) engine, but the rest of the digits are different.
On my build plate, it says "TYPE" is JNY720. "MODEL" says, KNLY720TUFI51. Also, it says the axle code is CA41. I also noticed the transfer case is divorced on this pickup. I've never seen that before either.
So, what would indicate a Heavy Duty" model in the build plate? I'm still not certain I understand that.