Lew, John, Jerry - if you add up all the things you each mention it does begin to make sense and very likely the reason for the thick gasket. I recall now how the QL (actually the Kohler "AQS") air cleaner was recessed at the back and partially fit over the carb (basically covered it up). This certainly doesn't allow for much air flow around the carb itself - but on the other hand the air cleaner had that rubber tube connecting it to a hole in the flywheel shroud forcing air, oops, allowing fan air to be blown into the carb, which should provide some cooling effect. However, I suspect it's not as cool as the old style exposed carbs - and maybe, just maybe, the gasket spacer kept the gas from boiling (credit to Jerry). So all of you get some credit here for why the gasket is thick. The question I still have tho is - what effect it has on engine performance, and would it actually improve performance on the older style exposed carbs?
Bill - I'm not sure I understand what you're saying about the brake pedal rubber pad on your 107. Does it have the cutout? It doesn't need it because of the spacer build up under the flat metal plate. And even if the metal plate was flat against the bent steel arm, the cutout would not be wide enough. Your bent steel arm has the twist at the right angle so the cutout in the pad would have to be the width of the steel. If you have the cutout in your pad it must have been replaced with the newer version (be on the look out for the Correct Police). If you don't have the cutout try and get us a pic of the side next to the tractor frame as best your can. I know you're a contortionist.
Someone out there must have a 1x6/7 with the rubber pad that does not have the cutout. Don't go peeling yours off to see but get us a pic if you can of the side towards the tractor frame. (If you peel your pad off chances are the rubber will tear and you'll need a new pad - and they ain't got'm withOUT the cutout - unless as Steve says, someone has the truck pads around).