Moving the trans cable bracket back will not help his problem. Its not like the stock system which pushes back on the linkage if you look when you mash the accelerator the trans cable is connected to the bottom of the carb linkage so when the carb is opening its pulling the trans cable out from the bracket because its hooked to the bottom of the carb linkage. If anything moving the trans bracket back could actually make his problem of the accelerator not opening all the way worse.
But from what I see the throttle cable itself if its adjusted all the way out so you can idle and then when mash it all the way down its only 90 percent it means your cable does not have enough length or travel using it with the new Bouchillon carb bracket they send with the trans cable kit.
Bouchillon also sells accelerator cables that have the extra travel to work with their kickdown cables I think that will solve your issue.