Just Plugging Along,

Yes that is reasonable with the Yamaha gauges they do alot more then I have figured out. The book that came with them is bigger then the book for the engines.
I don't think the Yamaha gauges will work with the Evinrudes, I would check to see what Evinrude has that will work for you.

Sounds like a good excuse to repower with new 4 strokes.

Good Luck,
Fishduck