O2 sensor will be in the exhaust, and you will have both a computer and a "buzz valve" also known as a frequency valve (an adapted D-Jet fuel injector) for pressure control on the fuel distributor rather than a simple pressure regulator.

EPA retrofit will include an EGR valve on the 77, i think.

Don't know about the oxygen sensor, but I'd bet you have cats under the exhaust manifold.

Is this device in the exhaust or attached to the engine proper?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!