Once I heard someone say that one reason they favored PPG is that PPG has the formulas for the early Z colors.  But the guy at my local PPG store begs to differ.  He DID have one early blue in the system, but it was titled "1971-72 Blue" so that is not at all helpful since 71 and 72 have very different blues.

Does anyone have the PPG Deltron formula, perhaps stuck to the side of a can of leftover 903 Universal Blue?

Is this a blue that was used for exterior paint? Not engine block paint, correct?

Correct...the exterior body color.

https://www.yelp.com/biz/williams-autobody-and-paint-san-mateo

These guys do a lot of the body work for the "historic racecars" that are around during Monterey Car Week, they might have what you need... if you get it do update us 😉

Per https://www.zhome.com/History/ZColorGallary/   this has the PPG codes to match the original Datsun colors. I'd really like to see my 115 blue Z next to a 903 blue Z.  In most pictures I cannot tell a difference.