Chevrolet's production report for 1972 shows the number of a given option sold and the number of possible Chevelles it 'could' have been ordered in. For the LS3, records indicate 20,031 were sold and an possible 605,289 Chevelles it could be ordered in. The 605,289 number is the total of all V8 Chevelles and Monte Carlos sold in 1972. http://www.firstgenmc.com
indicates that 1,268 72 MC's were ordered with the LS3 so one could narrow it down to 18,763 LS3's (20,031 - 1,268) in 424,470 (605,289 - 180,819 MC) Chevelles.
GM's Resto Kit only lists Chevelle & Malibu coupes, sedans, & convertibles (no wagons or sedan pickups) but it does state the 402 (Turbo-Jet 400) was only available when F78-14 tires or SS Equipment is ordered - so it definately includes the base Chevelle model. Ranier's Malibu 400 website, http://www.malibu400.com/
, has a 1970 base Chevelle (13437) with an LS3, Hugger Orange, and stripes. Site also has charts (from Dan Carr's poster) showing the statistical probability breakdown of the LS3 in 70-72 Chevelles so they were possible in coupes, convertibles, sedans, and wagons. No mention of sedan pickups however.