Would Witch be 72 or 73?
If you look at the seized engine from the First VC-160 you got, the serial will tell you the year of the base with the I
If you look at your MKIII engine, from the coast, that will tell you the age of the late VC-160 and it's base.
And I remember your MKI engine is 1970, and i can confirm the engine i took off that base (the one with only one post) was a 1970 engine.