Jerome Fine replies:
 I presume the LK201 and the LK401 are plug compatible?
 Also, what are the actual differences and why do you prefer
 the LK401? 
Yes, they are compatable/interchangable.  I've ended up with a LK201
attached to the VT420 on my PDP-11/73 somehow, but the rest of the VT420's
I'm using have LK401's.  I prefer the LK401's as they 'feel' better to
me.
I think the keys are slightly different in shape/angle.  I just wish they
had the flap that at least some LK201's have to put the piece of cardboard
that shows what the function keys are mapped to.
                Zane