Alan, I think you describe your issue clearly: your ability to adjust your sheeting angle (for different points of sail, and also when using different headsails) is limited by the location of your stanchions...and so, what to do about it.
What isn't clear to me is what you mean by 'beltings'. Are you thinking of attaching genoa track to a rub rail (usually some distance below the caprail & bolted horizontally thru the hull)? Or are you considering using the outside, vertical surface of the caprail? Or is there some third connotation for 'beltings'?
I would be wary of using either of the two surfaces I mentioned above. The track fasteners would, in both cases, be bolted horizontally & would see asymetric tension from the block thur which the sheet passes. Over time there will be tendency for the fasteners to bend and the bedding compound to lift
I have this problem to some degree on WHOOSH and my approach was to add an additional, stationary sheet block further aft (in my case, on the genoa track, but you could also place it on a fixed bail since it's position never changes). Thus, the sheet passes thru the forward (adjustable) block and then thru the stationary block before going to the winch
. The aft block's position was chosen so that the lead is always fair to the winch
, yet it allowed me a wider range of adjustment for the genoa block than if the sheet had to be led to the winch directly. It also kept the sheet away from the side deck
at the cockpit
coaming, improving the act of stepping out of/into the cockpit
somewhat. You might look at your own boat's geometry and see if that would help.