[SS Tim]

It probably is.
But there are several things you can look at the help confirm it is the original engine.

The engine assembly code is stamped in to the block just forward of the right head (below your A/C compressor. It consists of the engines build date and application suffix code. This will match your Protect-O-Plate and most likey be an original block (actually its one day's engine production of a specific assembly code, but that is as close as it gets). If you don't have a POP then a build sheet (not the glovebox door SPID) will give you a probable date to match. If that isn't present in the vehicle or a lot of work then compared the vehicle assembly month to the engine's, they should be close as in a 01/72 or 02/72 on the blue sticker. There are a number of threads on correct engine numbers and the locations of the stampings and casting number that a site search should easily yield for you.