I'm gonna go out on a limb here and say it's a Zodiac 420?
Reading the rest of the post I had a bit of a google and although I can't say what age it actually is, I can tell you that those engines were around in the late 1980's and boats bearing that style of tube are popping up from 1990. The catch is that both can be removed so the engine COULD be much older than the tubes and the hull different from either. A Zodiac person will be able to confirm the approx. age of the tubes - similarly a Yomamaha expert will put a close age on the motor. To my untrained eye, the whole rig could be 1990ish...
