Factory Intake or Replaced ?

[72 Cheyenne K20]

Hey Guys,

I just bought a 1976 GMC K15 that is the most complete and rust free truck I've ever bought. I'm probably going to end up restoring at some point.

I ran the engine suffix code and it is the original 400 C.I. enginewith a build date of 01/26/76. I ran the intake cast number of 346250 and it shows 76-82 All applications for a 305/350 and it has a date code of K245 (10/24/75).

The Rochester 4 B Qjet on it now is not the factory original. It's off of a 1973 something or other.

My question is: Could this be the factory intake? Is 3 months too far between engine build date and manifold production date to have been put together? Is this a correct cast number for trucks?

Thanks in advance and let me know what you think.

Scott