The windshield and non-opening 'vent window' suggest a late 80's early 90's GM styling hand. But the taillights with the slits beneath suggest a Chrysler connection - think 1st generation Intrepid.
Many Detroit-are 'job shops' banged mock-ups and prototype builds like this -many of which were displayed at the Detroit Auto Show, SEMA, etc. - which would jibe with the 'Joe's garage' feel of the building.