Details- the o2 sensor(s) go in the side or top of the collector anywhere between the last pipe branch and the long extension to the muffler. Do NOT put it in the bottom of the exhaust because depending on the climate where you live, upon starting, momentary condensation in the engine runs like a river on the bottom of the pipes and water is a sensor killer. Its kind of a tricky weld job to add the screw-in boss(es) while the headers are in the car. Use anti-sieze on o2 sensor threads.
Any electric fuel pump that's the same OD as a stock Ford electric pump will fit inside the stock tank (either early or late) thru the fuel sensor hole on the top. There are two identical looking fuel pumps- one for TBI-injection (14 psi) while the other is for multi-point EFI (50 psi). Dunno which Holley specifies. You'll need to add a sealed power wire thru the stock fuel sensor top to power any in-tank pump.
Mounted inside the tank like millions of other Fords since the late '80s, fuel pumps run much quieter and cooler. There's an illustrated POCA Newsletter article from about 15 yrs ago on this. I use mine as a carb primer or emergency pump backup.