Looking at the fuji track '05
 

Well, just one question. Is it possible to replace the sprocket on the back with another size standard sprocket, like the ones from harris cyclery? I mean, it's a standard hub+lockring setup, yes? And what about putting a freewheel sproket on, same deal?

correct

If you're orderig thisbike or buying without seeing it first, be sure to get the proper size. Fuji's are measured center to top of the seat tube/post. So a 56 is more like a 54.

the fuji track got some nice upgrades from '04. they switched from crappy ass quando hubs to much nicer formula hubs with cartridge bearings. but i would recommend replacing the cog they come with, because its a crummy stamped out one. id say get an EAI or dura-ace cog.