Just got my new EGR valve in for my `79 CJ5's 258, after no small amount
of frustration with my favorite local parts dealer (it went to the wrong
store). It replaces the one that was squashed at some earlier point in
the engine's history.

The instruction sheet says "look up the original valve part number on the
selection chart printed on the back of these instructions" to find which
orifice washer to insert (there are 6 different diameter orifice washers).

There is no part number stamped on the existing EGR. Anyone know the
original GM part number for the EGR for that engine?

The existing EGR doesn't have a washer restricting the size of the hole.
It has a 3/8" long tube that extends in the manifold instead, so comparing
them is kinda moot