1970 GMC C/M Series 4500-6500 Engines

[ClassicTVMan1981X]

In 1970, when GMC switched the 4500 to 6500 series from the H/J hood to the C/M hood already used by Chevrolet since 1967, in addition to the Chevy 292 straight six and the 350, 366 and 427 V-8s GMC still offered their 379, 401 and 478 V-6s along with the D478 and DH478 Toro-Flow diesel V-6s.

The conventional school bus chassis models (B4500 and B5500) were also part of the hood change.

Is it true that the 1970-72 (and 1973-74) GMC C/M series really had both Chevy and GMC engines available?

~Ben