The Demise of the L78 Option
Although the first known, documented, LS6 Chevelles were not built until early December the wheels were put into motion at the end of October. It isn't known when the last L78 or L78/L89 was built but this was the beginning of the end for the L78 engine option.
October 30th, 1969
TO ALL DEALERS:
Please be advised that effective immediately, the LS5 (yes, LS5) engine for Chevelles, El Caminos, and small wagons may be submitted for production. Also, new 360-HP SS454 option Z15 for Malibu coupe and convertible or El Camino, may be submitted with either M40 transmission, or new option M22 4 speed special transmission. Z15 includes same axle ratio and basic components as Z25 SS396 except engine. In addition, new 450-HP 454 engine may be ordered with Z15 as option LS6 immediately. Prices of these new options will be forwarded as soon as possible.
In conjunction with the release of LS6 450-HP engine, the 375-HP Engine Option L78 and the L78/L89 for use with SS 396 is in process of being cancelled, and further orders for these options should not be submitted.
Very truly yours,
Zone distribution Manager
This follow-up is generously provided by Mr. John Donchak
Fran Preve is the historian for the Tonawanda plant, I'm sure many on here either know or have heard of him. Anyway quite a few years ago he was authorized by GM to make copies of all plant and dealer production bulletins from back then. He graciously did some research for me earlier this year and confirmed a few things. Here's pretty much the timeline based on actual internal documentation - as opposed to the "GM did strange things" black hole of unverified claims.
The "Richmond letter" (shown above) as it's known was disseminated on 10-30-69 from Chevy to dealers stating: "...the 375-HP Engine Option L78 and the L78/L89 for use with SS 396 IS IN PROCESS of being cancelled..."
(On) 11-7-69 a similar letter generated from the Charleston Zone stating: "The L78 option IS BEING CANCELLED in view of the newly released 454 CID engines."
And finally on 11-20-69 a product bulletin stating: "With the release of the SS 454 engines, option Z25/L78 375 HP 396 V8, and option Z25/L78/L89 375 HP 396 V8 with aluminum cylinder heads "ARE NOW CANCELLED".
(On) 12-8-69 A plant bulletin was released stating " The LS6 engine is now in production."
While there were certainly a small handful of Chevelles rolling around facilities with LS6's prior to 12-8,these were R&D transplant 396 cars being emissions certified, as well as long lead press cars being evaluated by automotive journalists etc. These were crusher beta cars, not DOT certified, and never intended for production.
A GM exec who ordered an LS6 coupe as his zone demonstrator in October, was told by the Baltimore plant manager Earl Prentice that he was to receive the first one built at that plant, and the "Pilot" LS6 went down the line there on 12-9-69. There are documented examples of L78's built on 12-8, even though the RPO was cancelled on 11-20, so obviously there was a delay involved.