Again, ask the question to the Grand Banks Owners forum. There are people on that forum who built careers on the maintenance, repair, restoration, and upgrading of GBs and will have the answer for you.
I know that on the GB36 the settee-to-berth conversion was standard with the Hi-Lo table that was standard on that model until they switched to using the so-called "yacht table." The Hi-Lo table actually becomes part of the berth. We chartered a newer GB36 before buying our own and it had the yacht table. I don't think the yacht table helps turn the settee into a berth. But it might--- we had no reason to try---or it might be removeable to allow the settee to be converted to a berth.
But someone like Bob Lowe on the GB owners forum will be able to tell you.