Here is one post I saved.
http://www.valkyrieforum.com/bbs/index.php/topic,10426.0.htmlanother
http://www.valkyrieforum.com/bbs/index.php/topic,10066.0.htmlIn there is the link to the how to, but the internal links aren't there right now. I don't know if it is a temp thing or permanent. Photobucket originally had the pictures, and most don't work anymore.
I believe the 501 is a 5" speaker, and the original was to have been a 401 (4") which was discontinued. Any 4" speaker should be a bolt in.
BUT, I forget entirely, but the speakers should be a none regular 4 ohm speaker, not a 8 (or vis-a-ver-sa).
The posts where old, pre 2010, so a search should be your best friend, and fine something.
someone had a link/web site/something, that brought up old posts in forum. Maybe this could kind the old post and the pictures.