Emulation is very close to 100% cycle accurate for many, many machines. You would practically not deal with this problem anyway. Now, I may want to tinker with

Emulation is very close to 100% cycle accurate for many, many machines. You would practically not deal with this problem anyway. Now, I may want to tinker with my computer on a board level, making a period-accurate hardware-tweaks for the machine, how exactly I'd accomplish that, if everything is just a big FPGA? Now, having IC'level FPGA substitute for big chips on the original board is a bit better than one big flat fat IC, but it still a different machine and cannot be called C64, as much as a Ford-T is not a Ford-T if you put a modern electric motor to it, even if you tweak it to sound and handle exactly like T does.