GM-GMC: carburetor, gmc vandura, helm publications

Question
vacuum hose diagram, for 1979 gmc vandura 6.6 lit.rochester m4m, auto trans with air,charcoal canister...some one has replaced carb and i think they have rerouted the vacuum lines as this unit was converted from dual fuel propane/gas to gas only ...unable to find diagrams..also has rear vacuum break only


Answer
I can't help w/ that but here are two sources. If helm can't help Bishko can.

Helm Publications - Ordering 800-782-4356 and 800-551-4123


Bishko Automobile Books 440-338-4811  Bishko Publications Order Line General Helm is the contracted and preferred supplier, Bishko is only to be used when Helm cannot provide the requested services. Customers will be charged for the merchandise.