I posted the other day a link to 650B Palace’s list of 650B-compatible 26" mountain bike frames, but that doesn’t help much if your frame isn’t on the list.

Assuming you already have a frame that isn’t listed, and all you want to know is actual measurements for various 650B tires on the market to see if you have clearance, you can check out the shared Google Doc below.  The list originally showed up on MTBR.com, but I honestly can’t remember who shared it.

Link:  https://spreadsheets.google.com/

Also, if you’re looking for a 650B-compatible fork, here’s a thread on MTBR.com that will hopefully make it easier for you:

Link:  http://forums.mtbr.com/showthread.php?t=392220