From my research you can use the stock brake pedal and cut it down to size. That means you just need the clutch pedal more then likely. Everything else posted match's what I have seen for the s13. It can't be that different.
yeah, the gas pedal is the same, but the auto one has a kick-down button. mechanically theyre exactly the same, but you might want to eliminate a useless button, and some weight (buttom, bracket, wiring)
all KA, SR, CA trannys are exactly the same, at least in S14 and S13. the only differences are the bellhousings. and yes SOHC and DOHC trannys are EXACTLY the same. i currently have a 90 tranny on a 91 motor. so you need any transmission, and a SR bellhousing. or you can have fun trying to find a S15 tranny for a decnt price.
I would get a front clip if I were you, but they are hard to come by and are often expensive to get a nice one. The advantage though is that you will have all (or most) of the auto-to-manual swap stuff in addition to the motor, tranny, etc. This will also allow you to see how things are set up on clip, as an informal means of guiding your installation of the aforementioned things in to your 98.
All I have to say is: stupid Nissan North America for making so many 240's in automatic! I had a helluva time finding a S13 in manual.