Okay, so I bought a 2008 Rockhopper frame because it was a great deal ($30) and figured I would carry over what I could from my 1993 Yokoma Yosemite MTB (Deore parts). The hardest part is this BB/Crank issue.
I got the BB off the Yokoma and tried to put it on the Rockhopper, but part of the threading was hanging out the Rockhopper tube. The BB seemed to be the same total length (126mm long) as the Rockhopper BB is listed (68 x 126mm) and the threading fits perfectly, but the problem is this; the Rockhopper frame tube that the BB goes in is 2 10/16" (~67-68mm) and the Yokoma tube is 2 13/16" (~81mm) long. So a good chunk of the threading (3/16") is sticking out of the Rockhopper tube.
So I can get the recommended Shimano BB for the Rockhopper new for really cheap ($13 shipped), but it is Octalink whereas my old Deore crank is square taper. My whole goal in this project was to make a new bike for as cheap as I can (with decent parts) and buying a whole new crankset to match the BB is my last option.
And yes, I can only assume that some of my explanation demonstrates that I am not a skilled MTB mechanic. I am simply a novice that is enjoying a fun project. Thanks for any help!