The bulkhead end of the sill rail is a fixed bracket. The tub end has a separate bracket that you bolt on.From my understanding the 90 and 110 hardtop have the same sill setup. Where is the adjustment? It is all bolted to the tub and the seat box which I have not removed.
Poor image, but you can just make out the rectangular slot on the right hand side that the upright bracket bolts through. This gives you enough adjustment to play with washers on the bulkhead to outrigger bolts.