I am unable to make sense of what your picture is trying to show. But from your description, I will offer this.
I keep my boat on a Hydrohoist lift. The bunk supports are attached to the lift in a triangulated manner to prevent rotation and falling over. Under the carpeted wooden 2x6 bunk lying flat at a slight angle to follow the hull shape, is an angle iron running full length from bunk support to bunk support for an approximate 16 foot length.
I would suggest looking at their web site to get an idea what that manufacturer does, then look to see if your lift maker supplies something like it. I guess you have learned that this is a good item to go heavy duty.