311 L-89 Camaros is pretty much accepted gospel per the Camaro reference books over at least the past twenty years. Here are actual page scans from four such books:
Big Book of Camaro Data 1967-1973 (1995) - Page 47
by John Hooper:
Camaro (2002) - Page 55
by Steve Statham:
Gm Muscle Cars (2002) - Page 50
by William G Holder, Phillip Kunz:
Camaro - (1995) Page 40
by William Holder, Phillip Kunz, Phil Kurz:
What might explain the L89 Nova confusion is the excerpt below wherein the authors apparently confused Camaro numbers for Nova numbers:
Super Chevy's Nova Handbook: Restoration and Performance for 1963-1967 Chevy Novas (2000) - Page 10
by Super Chevy Magazine Editors:
