Dear xbuckaroo05x--  According to the boys at Crutchfield, you can use a 6.5 to 6.75 inch speaker in the rear doors of your blazer.  Take a look for yourself at--  http://www.crutchfield.com/S-ljPlgW4QKsW/cgi-bin/prodgroup.asp?g=400&l=D&cc=01.   Good luck from Bovan.