I've completed the mechanical sync between the two carbs which looks fine at idle... the one item I noted is that at full throttle I now have a little slack in the cables, is this common? or do I need to redo the mechanical sync?
Yes... it has the stops that slide over the cable. I was at OSH and took at good look at your engine setup, cowling clearances and muffler mod. I did note that your throttle & choke cables were different from mine... they have some kind of coating or covering.