Section 24007 (b)(2) of the Vehicle Code states it is the responsibility of the seller to provide a valid smog certificate at the time of delivery of the vehicle. You could inform the seller of this Chevy Blazer that the truck will not pass the smog check and see what sort of amicable resolution you can come to.
As far as the Blazer's smog check failures, the Edelbrock exhaust headers need to be stamped with an OE (executive order) number by the California Air Resources Board (ARB). Without an EO number the headers are considered to be "tampered/modified". The solution in this case is to find a pair of original Chevy Blazer headers from a wrecking yard (for a 1984) and have them installed.
The EVAP fault on the order hand will require hands-on diagnosis. The EVAP test ensures that there are no vapor leaks in the hose(s) between the Gas Tank and Charcoal Canister. The EVAP test tool calculates any drops in pressure due to any leaks. The fix requires locating the vapor leak and repairing the line and/or component which is defective.
