How Rare is this Shamrock Green '79 Silverado?

[CircusWagonJim]

Hi guys. My buddy and I have been buying some trucks we think are interesting and I wanted to get your opinions on this truck and if it's what the seller told us. First off it's supposed to be a very rare color- Shamrock Green Code 43. Was told only a handful were painted this color- and even less with a white bucket seat interior!
You can see it came with some pretty good options-
Silverado
350 V8
Auto trans
Cruise control
Tach
Tilt
Buckets and Console
Power windows and locks
Sliding rear window
Deluxe bumpers
AM/FM radio
Int. wipers
Chrome grille

And I'm VERY thankful that with all those options it still has the small cool exterior mirrors- not the ugly jumbo ones.

Now my question is are the buckets added or original? They aren't on the SPID, but what is the last item- XMM4 MYSTIC VIN?