Mate stick to the same thread, it’s hard to track your plans. AGP 8X is physically compatible with AGP 4X as most cards have “universal” connectors. The shorter the cable the better.
Still not sure where you are going with this; you’ve not going to fit a power hungry QS, MDD etc inside a 63xx case without it being frankly, an exercise in frustration and waste of money and time. These cases are cheap and plastic prone to snap. Keep a good 6300 for OS 8/9 2D games and a G4 tower alongside.