I have a Zodiac Pro 420 fitted with a 40 Hp Honda 4 stroke, both 2005. In terms of parts for the rib, dont worry, they are still in production and you can buy anything you want for the rib from a drain bung through to a new console or tubes etc. Loads of Zodiac dealers can get you parts if needed, but save up first, if its boat related add a few zeros on the cost......
For example - Chas Newens Marine-Boat Hire-Boat Film Hire-RYA Training
and also - http://www.zodiacmarine.co.uk/
The engines i'm not so good with but by the looks of it its not that many years old and parts should be readily available. Again there are a few businesses on here that will help you out or your local outboard dealer will be able to get parts easily.
(EDIT - Just seen the main site and that its listed as 2006 - You wont have any issues with parts for the engine at all).
The actual boat itself is really good. Im certainly very pleased with it and it got a lot of use last year. It handles well, is comfy and certainly zips along with the 40 on the back. With the setup i have allows for sitting or when bumpy standing with ease.
A friend of mine also bought a Zodiac Pro 420 and is really pleased with it. He has a 50 2 stroke mariner and it does have the edge over me but he also uses a lot more fuel doing it.
Here is a link to a quick video of the two of them.
There is also this one i found which was taken by a passenger on a day trip when we tagged along
but it gives you an idea.
You will see on the way back the chop got up a little bit and i had to stay in the wake of the larger boat. The Zodiac could handle it with ease but just not at the speeds the two others were doing as it would have been too dangerous both for me and the boat.
Overal, really happy with the boat and you wont be disapointed if you do go for it. I'm sure there will be a few more ideas on ribs coming your way soon from other members too, just comes down to what you want. Its up for £6250, thats what i paid a year ago for a virtually unused boat and engine which had about 20 hours on it. I reckon given the current climite theres a deal to be done there. Any other questions ask away.
Couple of pics for good measure too