Sure they are collectable. In 1998 Marshall made 100 of the Orange Crunch amps Worldwide. The owner of the Marshall Museum who is on this forum could tell you more then me. (Sigi M) but I believe they are simply a standard DSL.
Here is a link to the ones he has in his museum.
http://marshallroadhouse.com/viewtopic.php?f=39&t=11967