Having mot half an hour ago finished pulling a pedal box out of a 20 I can tell you a number of things. It took me about 30 minutes (using air tools) to remove. Three bolts holding steering column, three nuts holding on wiper motor (pray to god you never have to change one of these) and the bolts holding the forward end to the bulkhead, for this car it was five nuts/ bolts, your's will probably have three or four, as this one had been modded. Disconnect the brake light switch, the clutch cable and brake MC pushrod, then reef, pull, twist and generally root around until it comes out. I also removed the attach bracket that goes between the steering column, and the PB.
You may also want to remove the dash for better access to the top bolts, add 5 to 20 minutes for this depending on who's been at the car before you.
Installation is the reverse, and will realistically take about twice as long as removal.
*Disclaimer: These times are a rough guide. I used a rattle gun and an air ratchet on everything, have access to good tooling, and I know my way around a twenty fairly well. *
Hope this helps.
R