Re: Anybody have a diagram?
There is a remote possibility that someplace there is a diagram of the plumbing....but.
After being in the industry from long before that time I can tell you there were rarely any plans or diagrams, plus things like this could be done differently by each person assigned to the task, or changed weekly as needed for the type of equipment they purchased that month.
Even if there was a diagram it may not even be close to accurate due to how things were done back then (and still done by some builders).
I'm a little confused as to why you think 88 random boaters would know more about this than you do, probably none of them have a Ranger boat, and for a fact I can tell the chances of one of them owning or needing to know this info about 1978 Ranger would be very remote, lottery odds or worse.
If you wait patiently someone may still be able to help you though.