still having problems

aight, got some alpine type r 6 1/2's for the front doors, and some alpine 6 x 9's for the back. i got the front ones in w/ no problem but the back dash is still giving me some problems. i have gotten to step #3 of the IMPORTANT: thingy, but im afraid if i pull the slots that hold the seatbelt down any farther they will break. i cracked the plastic thing around the seatbelt already trying to get it off but no such luck. if anyone could give more detailed instructions that would be most appreciated! and if anyone has a set of type r 6x9's in the back, i would like to know how they sound since i cant put mine in yet. thanks a bunch