Haven't done it on a 4.2 but have on a 4.5 and a 5.6 so the set up is similar. To get the third bolt, the hidden one, start under the car and come in from behind with a 10mm socket and extension (1/4" drive set). You might need a universal joint too depending on how tight the other accessories are to the housing.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.