Norm,
A connector like you show is alright, but you might consider using a terminal block with screws. It is more reliable and easier to work on - those Molex connectors need special tools, not just a screwdriver. I would go with the connector if it is already on the harness, otherwise I would use terminal blocks, one for each engine.
You will need at least eight connections per engine: Ground, battery, ignition, start, alternator, tach, fuel, and temperature. The voltmeter connects to battery so it doesn't need its own wire. It is nice to have spares, I would use a terminal block with 12, each engine.
I can mount the terminal blocks to the back of the panel, wire to them, and give you the eye terminals needed for the wires that you will hook to them. They are easy to put on, the connectors not so easy.
As you take wires off, mark them with masking tape. It is a zoo trying to figure out which is which. If they are properly marked, then putting them back is no big deal.
I wish I had a picture of the back of my panel to show you, but when I am doing stuff I forget to document it. Next trip to the boat, will do.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida