To quote kmself@ix.netcom.com, # - twm is a pretty minimal window manager. # - blackbox and sawfish are both pretty slim.
I love Sawfish, but I don't think it's appropriate in this case. Almost all of Sawfish is written in the Rep dialect of Lisp, and is interpreted at runtime. That's a CPU-dependant task. Given that this is for a 386, I don't think it'd be a good idea. But, by all means, give it a shot :)