Talk to these guys.
Hamilton Engine Sales
5540 N.E. Columbia Blvd.
Portland, Oregon 97218 Craig (503) 280-1353
These are industrial/marine engines and the highway trucks use the same engine but different part number system and the two don't talk to each other. Craig seems to know as much about these engines as anybody I have run into.
What info you can find about the dash wiring will be in any GM light truck manual but if you look back through the forums the wiring under the dash is always a mess having been heavily modified by Airstream, previous owners, service mechanics and anybody's guess who else.
"Socialist governments traditionally do make a financial mess. They always run out of other people's money. It's quite a characteristic of them."
~ Margaret Thatcher ~