Engine Serial Number T54Z

1954 Chevrolet Passenger Car 235 Engine ("Regular car Engine") made in Tarrytown, NY

As to it being original or replacement engine, an original registration document might help answer that question.

What is the head date casting code and the block date casting code?

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.