Jim,

As far as the Chevelle is concerned, the switchover appears to have been around the first week in December 1969. The Baltimore plant appears to have been the last plant producing L78's based on buildsheet data collected. The sheets that have been collected are all customer ordered cars, and it appears that the plant was anticipating the stoppage of the option. There are 2 sheets that indicate "L78" in the RPO coded section, but also include both the "SS396," and "SS454" codes as well. These sheets are from 12-4. There is another sheet dated 12-8 that shows only the "SS396" RPO so it is quite possible that the plant had a better idea of LS6 production startup dates. It also appears that the Baltimore plant was the last plant producing L78's as all of the later cars (after mid. Nov. '69) appear to have been built there. I speculate that it might have something to do with wanting to use up as many L78 engines as possible, and the plants close proximity to Tonawanda. There are a few memos (from the fall of '69) that show the L78 option was being canceled in favor of the LS6. The timeline seems to support the dates involved, as far as when the option was actually canceled and production ceased.