The current owner converted the boom to a jiffy reefing system. Does anyone have any pictures of the original reefing system around? I am not sure I would want to restore it but I would like to see how it works.
If the boom hasn't been replaced, then the roller reefing bits will still be there. Not much to it - the topping lift and mainsheet will be fitted to either end of a plate which is fitted to the centre of the aft end of the boom such that the boom can rotate. The front end of the boom is fixed to a shaft which runs forward through the mast with a handle fitted to the forward end. The actual handle bit folds down so that it locks into a notch in the mast to prevent rotation. I don't think that you would want to revert. See this thread on booms http://www.bluemoment.com/forum/viewtopic.php?f=1&t=5223
The second question is, how well does the MD6A engine hold up to 40 years of salt water cooling? This boat is in the water year around.
The biggest worry would be that the cooling passages are blocked / restricted by crud, reducing the water flow and reducing the heat transfer.
I cleaned out some of the gunge from mine using brick cleaner - the acid based one - not the alkali one. You need to take appropriate precautions for yourself and your surroundings. You would need to remove the thermostat to prevent damage to it, and you would need to set up a circulation system - works better if warm.
Does the boat still have the combi gearbox fitted to the MD6A? It's an added complication if it goes wrong.
Does the 6A still have the Dynastart? Is this the only means of charging or does it have an alternator too?
A lot of Vegas will have been fitted with the 13.5hp Beta BZ482 engine and conventional gearbox. I spent about £5,000 in 2007 fitting a Beta myself after living with the MD6A for 3 years.
Ask again if you more details about any particular aspect.
Edit Nick posted whilst I was still composing so some repeated info but I haven't bothered changing my post.