The second owner rigged the boom with a double mainsheet arrangement that he saw on a Mirage 25 which works great for setting the boom
and the sail where you want them. The advantages, which are similar to the control provided with a more expensive traveler, are:
While beating in heavy winds you can trim the boom to windward, ease the main sheet to put twist in the main sail so that the top is eased
downwind and spills some of that overpowering wind.
While beating in really heavy winds you can depower the entire sails by trimming the boom leeward keeping a consistent flat mainsail,
with a little luff in the entire leading edge.
Off the wind you can use the leeward sheet only to get a more directly downward pull on the boom, and a flatter more powerful
The disadvantages are:
This system might require a little more tweaking after tacking to get the boom right where you want it. But you have that same issue
with a traveler to adjust it after a tack (unless you had the traveler car at centerline already, in which case you really were getting
no benefit from having a traveler).
It will take more care before jibing to make sure you have slacked the appropriate sheet sufficiently to allow the main sail to
change sides. Again you have that same issue with a traveler, to re-adjust the traveler car to where you want it.
Concentrating the attachment at one point could result in a very high amount of sheer forces concentrated at one point on the boom.