Engine & Tranny Installation-Dougs Headers, Poly Lock Mounts, Nothing Fits!

ok, thats one problem im facing...the next is i cannot get every bolt into the header...5 of the 6 bolts thread into the head, the 6th one is very tight and will not go. i just need a little bit of wiggle room then it will go....ive tried unbolting the header and installing each bolt differently in different orders, but it seems the bolt holes in the headers are off just by a hair...would it be possible for me to chamfer a couple holes in the flange? just very slightly enlarge the holes at a vey minor degree to get it to go?