GMC V6 engine info

[gsmeier]

I am having a problem ID-ing the serial # on my GMC 401 cu V6.
The serial # is as follows: 401-011246. It is stamped on the passenger side front of the block close to where the head meets the block. What year is this engine?
Does anybody have any info on these engines?
Auto parts stores don't even list this engine for tune up parts. Maybe I'm looking under the wrong truck size/heading. What size trucks did these engines come in & what years did they have/make them? Auto parts stores have the 305 V6 listed. Do they take the same points, condenser, cap, rotor?