the 400 axle is a slightly larger diameter to normal square taper axles, so you will have problems finding a longer one if they actually exist. it took me about 6 months to find an axle for my 400s. you could use the spacers to stop the crank hitting the chainstays then use a coke tin to make some shims so the cranks will tighten onto the taper. this was my method i used before i found the correct axle and was using a generic square taper axle, it worked fine.