Interesting thread on at least a couple of counts - I own a couple of Wals, and the last poster has the same name as me.........
There is no Wal Mark bass but the three Series of Wal Custom basses are loosely referred to as Mark I, Mark II or Mark III models. Somewhat oddly some people do also refer to them as Mach I, II and II respectively, though I've no idea how they relate to the speed of sound....
Steve Chesney's site mentioned by Matt has some info and the Yahoo club at
http://groups.yahoo.com/group/walbassesnaturally/ is another source of useful info and helpful people.
Again, as Matt has said, Wals are English made and bolt-on in nature. They're built to very high standards and offer extraordinary specs, especially in the electronics department. While there's no direct Wal/Alembic connection the Wal Custom preamp is not unlike the Alembic 20th Anniversary circuit, two lo-pass filters with 2-position Q's, but also with a hi-mid boost around 3kHz and pickup pan and with quite markedly different frequency ranges and boost amounts.
Another more tenuous link revolves around Mark King of Level 42 fame who was supposedly shopping for a Wal when he came upon a Jaydee Supernatural - another excellent English bass which he subsequently bought and championed. Jaydee's have often been likened to Alembics in terms of body design shapes and aesthetics.
Mik
