If you do a search on 'Avon Adventure 4m', then you may find some info on the boat listed in post 1. Avon didn't brand them 'Adventure' back then, but it's the same boat.
Blackroady on here has one with a Yam 4-stroke. May be worth asking him - I recall he quite likes it for pottering about on.
Problem with 4m RIBs is the lack of deck space, especially when they're rigged as this one is. If you could find something nearer 5m, then you'll probably find it better suits your requirements.