google for it
or buy paper bound Service manual. off ebay used and rare !
vacuum varies by if car is calif or federal car. USA< or export model.
3 kinds for 3 kinds of smog laws 1979
sorry there is no other ways.
Chevy has no answer now. this old .
the online manual
shows 6 vacuum maps for one 250 engine
for cal/fed ,and light and medium duty ratings
sadly will not zoom and be clear
the online jokers scan a real book and messed it all up.
no digital books then so must be scanned, and correctly .
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