1980 C10 Inline6 250 Carb vacuum and brake booster

[D13]

OK, you have an integral head with the staged 2bbl carb.
The brake booster feed comes from the intake, yes, but you need a check valve in between. I'll see if I can remeber where the vacuum source is.
The big pipe on the front of the carb goes to the evaporative emissions cannister.
One of the hoses goes to the air cleaner thermal switch.
If you still have an auto trans then you'll need to get that cable hooked up.
You're missing most of the PVC system. There was a thread a couple of weeks ago about restoration of a 6 with all ther emissions, showed some of what you're missing.
You are going to desperately need a factory service manual - NOT a Chiltons or some other book.