The decal on the radiator support is the only place I've seen the "letters" and numbers ID'd,and tell where each vacuum hose hooks too..no book I've seen has a breakdown of them,and I have quite a few GM tech books and parts catalogs,maybe you can get vacuum hose diagrams from Chiltons and other sources by special order too,or perhaps at yout library..I found one Chiltons book for vacuum diagrams at a town library about 5 miles away that has saved my butt many times.but it can only be used at the library..though you can make copies of the pages needed..
I sometimes luck out and find a truck in the boneyard the right year and engine with an intact emission hose routing decal..we used to get calls at the junkyard from people wanting to copy the diagrams on many 70's cars,there was so much "spagetti" under the hoods those years!..some collectors far away had us take a close up photo of it,and mail it to them,and they would send us some cash in return..
In my experience,the PVS (ported vaccuum switch) in the thermostst housing is for the EFE Valve (heat riser),and some have 2 other ports that go the the distributor vacuum advance...the other PVS located in the intake manifold usually runs the EGR valve,but I've seen some with 4 ports,and couldn't say for sure what the other 2 ports are for,but I think they also control the spark advance possibly...plus if your in california,everything is different there emission-wise,as far as how everything is plumbed up,or what is used ..
I liked the 50's best!..NO emissions!--and NO confusion about where to plug all those hoses onto...?
