Can there please be a section like "slots" but "antiSlots" where when specified parts are listed that can't be selected/equipped anymore. This will bring the game in line with what people would expect. You've selected a longer chassis? Now the selectable driveshafts are all only the right length. This would also mean you don't need to do the split chassis trick thing you've done on the new t-series. It will work with so many configs, like bigger engines will fit under the right bonnets (instead of clipping), and auto/manual shifters will also be correct. A lot of this will probably require "coreSlot"s set to true, but maybe when the part is selected, run some code that will do a slot check, and instead of just un-selecting a part, specifically put another available part on too. Because multiple separate parts could deny parts from the same slots, it'd have to make a list before the check is done This is not the same thing, but if you could also have a section that has a "preferred slot parts" thing, where when a part is put on, it finds the specified slot, and puts the specified part on. (these sound similar but will offer different functionality for mod makers)
