Nice! I did one myself but made all the pieces myself including the wheels! It added to the time line but was a lot of fun. My 2 x 72 can be seen here:
2 x 72 inch Revolution Belt Grinder (aka The Metal Muncher!)
If your like me, next you will be building all kinds of accessories to go with it. I did everything but a buffing wheel and surface grinding attachment. I too did the 7 inch wheel and it's CRAZY fast! Too fast I think, I usually run only about 1/2 way.
I see your trying to control the dust. That's a big issue with these! I take mine outside every time I want to use it which is a pain. I was thinking of building a tent over mine but I like your idea of a box. Rig in a shop vac and you might just have something there!
Well, don't let me keep you, get back to work. lol