Just did a number of searches on the net and only found Boss 351s...no 302s. I worked at a Ford dealer in the mid 70s and found then that not all there manuals were correct. They would come out with a revision after realizing a mistake.
People keep turning up evidence that Ford planned to continue the Boss 302 into 1971, but for some reason cancelled the idea fairly late in the planning stages. So occasionally literature and stuff that was printed "early" pops up that mentions the engine or car. There are even pictures out there of the 71 Boss 302 (in development) that never was.
Somebody somewhere knows the story behind it, but I haven't heard it.
Ford intended to use continue the Boss 302 into the 71 year. In the Fall of 70, the program was nixed in favor of the Boss 351, my guess would be due to lackluster performance in the bigger body of the 71. The literature was already printed for the 302, and a lot of it was distributed already. I've seen NOS Boss 302 fender & trunk decals with a D1Z part # on [censored], authentic? I don't know, but it did happen. The Osborne reprints fo the 71 body assembly manual shows some prints of the Boss 302 that are "X-ed" out and superceded by the Boss 351. The tire inflation decal on my 71 Mach lists both a Boss 302 & Boss 351, and it is original from 12/70
The Boss 302 was dropped in favor of the Boss 351 because Trans-Am racing removed the 5 litre limit. That allowed Ford to go to the larger engine which was more appropriate for the larger body 71 Mustang