SPO vs RPO... Government Blazer question

[Metrodps]

OK what is the difference between S.P.O. and R.P.O.?

Would it mean special production order vs regular production order?

Reason I ask is this:
Y06 : RING GEAR, 9.50 IN., SAGINAW, (S.P 0.)

 

[Metrodps]

Almost 20 hours later and no one knows must be a record!

 

[Metrodps]

TTT! anyone???

 

[BadBob]

I just happened to be digging through some ancient stuff earlier, and saw it mentioned as "Service Part" something or other.

There was a label I remember seeing though on a truck at some point that said something like "Chevrolet Special Equipment"

 

[Metrodps]

Reason I ask is this:
Y06 : RING GEAR, 9.50 IN., SAGINAW, (S.P 0.)

It is on the Government K5 that I have no it is not a M1009 I believe it was a police rig. The Caprice Cop cars had the same Y06 info too. So I think it is a unique thing.