Adam supposedly picks up $20M in cash. That would be 200,000 in $100 bills. Each bill weighs about a gram, so that would equal 200,000 grams or about 441 pounds of cash. It would also take up over 20 cubic feet of space, which would completely fill Adam's Dodge Challenger's trunk, and then some.
The used DNA to match the bodies found in the forest with people that disappeared during the late 70's. DNA wasn't put into a database or recorded until the '90s.
The flashback to 1975 has Disco Inferno playing in a club, but the Tramps released that song in 1976 and topped the disco charts in 1977.