Hopefully I will not start another round of 'Shock Wars' on this post.

I have an '88 Westy and recently replaced the 5-yr old KYB shocks with
Bilsteins.
Here are my observations:

Please note that these are for an empty Westy.

The rears looked similar, however on the fronts, the KYBs had a minutely
larger rod and slightly larger case. The Bilsteins had a longer case. If
I had any critique of the Bilsteins it would be that the mounting heads
are only welded in two places to the shock body, making it look like a
potential place for failure.

As far as ride, there are differences, but for me, not the huge
differences that I was expecting given that the KYBs are about half the
price of the Bilsteins.  The main difference I noticed was that the
Bilsteins feel very matched front and rear - while I always felt that
the KYBs were a little bouncy in the back and undershocked in the front.
The KYBs seem to be initially firm to any bump and less firm as you go
to the end of the travel. The Bilsteins are opposite. They are pliant on
small bumps and firm up as the bumps get larger.

I've seen notes that the Bilsteins are firm/harsh, but I don't see that
they are any more so than the KYBs.

I have to give my preference to the Bilsteins. But I'd say for the most
part the differences are rather subtle, with the exception that the
front is much improved over the KYBs. I think the characteristic I like
the most about the Bilsteins is that it gives the suspension a more
precise feel.  But I also have to say that in retrospect, while not to
my personal taste, the KYBs were competent (particularly figuring in the
price) - but a little weak in the front.

Todd
'88 Westy