I have a Universal branded (real cheap 'n' nasty) mtb that I want to upgrade and use as a stealthy single speed commuter(it's the right size, has horizontal drop-outs etc).

Now, I was wondering, am I going to have problems with the bottom bracket and headset?

The only reason I ask is that these cheap mountain bikes have weird components(for instance, it has some kind of threaded headset and a cheap high rise stem, compared to threadless on most higher priced mtb's)

How do I identify what kind of headset/bottom bracket it has and whether it'll be able to take a better stem/crankset/handlebar etc(low/mid level shimano or equivalent)

Has anyone else converted a cheapo mtb into a single speed, how did you get around these problems?