There would be no point in a CUDA switch that was not accessible when the Mac was ready to run, ie fully-assembled but not closed. Many CUDA switches are in obscure positions, but accessible they are, even if that means that a handlamp and a non-conducting stiff thin rod have to be used to reach them. They are often close to a daughter-card slot, not least because hardware upgrades necessitate, in best practice, that you use the CUDA switch as the last act before you close the Mac, and processor upgrades are chief amongst such upgrades. It is probably of no consolation to you that you have now learnt several things: that 8100/8500/9500 internal plastics become extremely brittle with age; their PCI (8500/9500) card retainers are perfectly bloody (often yours); the MLB is a horror to remove even for trivial tasks such as battery or RAM replacement; and the CUDA switch has to be accessible readily, if not easily.
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