As others have said, it's a stock 400F header. These are direct bolt-on for the 350F (see my avatar) and will clear the oil pan with no problem when mounted correctly.
The peg set up for the 400F is different, however. Stock CB400F pegs will bolt right on to the 350F but the pegs sit behind where they mount -- on 350Fs they sit in front -- so it moves the pegs back about 6 inches. There is still plenty of room for the rear pegs (although the stock 4-4 pipes on a 350F mount to where the rear pegs mount and include a tab to keep the rear pegs in position. You've got to crank them down and be careful without this tab as they can still move, like if a passenger tries to stand up on the pegs). The rear brake lever is also different on a 400F, and designed to clear the collector from the header. This will also bolt right on to a 350F. I have seen 350Fs with stock pegs and stock brake lever, but the brake lever is usually at a crazy angle to avoid hitting the collector, and thus isn't natural for your foot position. The kickstarter is the final piece of the puzzle. The stock 350F or 400F kickstarter won't clear the 400F peg if you go that route (even though the 400F peg folds up for kickstarting). A CB550F kickstarter will, however. I've done this on a couple bikes, on others I just relied on the electric start. I told this to someone and he counted the teeth on a 350F kicker versus a 550F kicker and told me they weren't the same, but like I said -- it has worked for me.
On the other side, the 400F peg will mount right up and similarly set your pegs back a few inches. The 400F peg on that side has a shift linkage that bolts right on to where the 350F shifter goes, although sometimes you have to fiddle a little with it to get it to work well (and I've shaved off a little of the linkage to make shifting smoother on some bikes). On that side, the small loop on the kickstand will interfere with the shifter -- the kickstand on the 400F is mounted farther back -- so I have shaved off that loop from the kickstand.
I mounted a 400F muffler, just using a piece of angle iron shaved off and because the angle wasn't perfect I made a small angled bushing out of a skateboard truck bushing so that it tightens up snug. This was in 1997, and it's still going strong.
I also never had to rejet for this different exhaust, using the stock airbox and filter set up.
So the question is whether you want to go with the 400F exhaust -- they are definitely cool -- but fork out for the peg, lever, and linkage set ups, or switch to a different exhaust with the stock pegs. I am guessing they'd be about the same unless you found a cheap used exhaust. People sell the 400F pegs for about hundred bucks (maybe cheaper -- but you want to make sure you get the complete shift linkage), then you've got the brake lever and kicker.
