We don't want to try to just stick any old 82284 in - we need a CMOS version, since we're clocking things slowly. Luckily 82c284's were made, like this one from Intersil. The 82c284 can take a clock input as X1/X2 crystal inputs, or can can take a simple externally generated clock signal on its EFI pin. How you tie the F/C pin determines which inputs it uses. We'll be letting the Arduino drive the clock via EFI, so we need to use a pull-up resistor on the F/C pin.