Obviously it needs a new speaker. I was wondering if the Blackhawk would give me a clear tone with a tight bottom end that will let the Marshall sound ring out? Also, do I have to worry about it actually fitting in to the cab?
I don't know much about the Blackhawk,but I put a Celestion CL-80 in mine and it does all the things your talking about. The speaker was an easy swap, plenty of room and clearance. Check over on the Marshall Amp Forum, theres lots of info on speakers for the DSL 40C.