Shimano 6sp

Is there more than one type of Shimano 6sp or is it all
intercompatible? I've heard that this was a standard class of cheap
Shimano groupsets and therefore that chains, chainrings, clusters etc
from one Shimano 6sp bike ought to work on any other one.

I want to take some bits off one old clunker MTB to fix another
clunker MTB and would like some assurance that this will work, that
I'm not going to find myself half way to uni with a broken chain or
toothless chainring or something because I'm using incompatible bits.

I took the bike for a round the block test ride and it seemed ok,
though a little noisy. I suspect I need to adjust the gears to deal
with the noise, but I want to be sure because if it breaks I get
stranded 20km from home...

Travis