assuming you're looking at the closeout frames from jenson?
it's basically an ellsworth atlas/isis rear end (not exactly known to be the most durable or stiffest rear ends) with the eastern front (from wherever it's made) and comes in the 5" and 7" travel versions. the 7" frame front end is a bit more gussetted than the 5" version....
http://www.eastern26.com/
why don't you e-mail them and ask? stock fork on the frames is a bit over an inch difference in crown to axle height. may gank up the geometry or not, may void your warrantee or not, may mess up your headtube or not. i'd not want to put more than 180mm on the 5" travel frame, and might be nervous about even that. stick a good 6" fork on it and it'd make a ripping beefy trail bike. 8" on the 5" frame would be uh, stupid.