Actually, the Lark's consist order was changed at around the time the Espee lost the mail contract, I think - September 1967. The sleeping cars ran at the front of the Lark as well as the Sunset when sleeping car service was restored in 1970 on the latter. My guess is that demand for sleeping car space was fairly predictable, and the need to add or subtract cars was mostly due to demand (or lack thereof) for coach space.

I seem to recall also in Richard Wright's book on the Daylight that boiler equipped Geeps were used as early as the mid-60s. But I could be mistaken.