Mike, lower two bolts are studs that go into the leg at the bottom mounts (solid mounts) and the top two are hex head ones. they are not hard to find brand new. Give Greg at GB Watersports a call next week (hes on holiday this week)
The others are simple enough, you have 3 bolts around the back of the adaptor plate that bolt it to the leg and you have I think 5/6 long'ish studs attached to the bottom of the powerhead which go through the adaptor plate and bolt to the leg (as if the adaptor plate is sandwiched between the powerhead and leg)
Your better off getting new ones as old ones are already half rotton.
they have a really good catalogue system with exploded drawings of everything and all the Mercury part numbers for all the parts shown.
Does that make sense?