I suppose that it would make sense that all of AT&T's leading edge projects would use research Unix. I've always heard of the original C++ to C translator but this is the first time I've actually seen it.
In case you’re interested, Bjarne Stroustrup has been helping me collect early versions of cfront here:
Previously we had located a listing of Release E (which we scanned), source for Release 1.0 of 10/10/85, and source for Release 3.0.3. From these 9th and 10th edition snapshots, cfront 1.2.2 6/10/87, AT&T C++ Translator 2.00 06/30/89, AT&T C++ Translator 2.1.0+ 04/01/90, and AT&T C++ Translator 2.1++ 08/24/90 join the list.