You did that old boat proud bro...

FWIW my MSD and relays are mounted exactly like yours....

As for the solenoid....One large lug goes to the battery, the other large lug straight to the starter motor, the "S" goes to the ignition switch and "I" goes to the ballast resistor or "+" side of the coil if resistor is used, if not resisted, leave empty...
If one of the smaller terminals says "G" it needs to be grounded, they made them both ways...

GT