T-case to frame please help

[Dads 68 GMC]

I took a mounting bracket off a `69 blazer today and bolted it to my frame,now the bolts that go in the right side of the T-Case will not go in.I took the upper transmission mounts out & they almost line up. the mounts seem too thick,they are 1 1/8in.thick I called Carquest they only show one from `68 to `81.pn#31-2107 which is what I bought. Maybe i have to drill holes in my frame? I would appreciate any input,Thanks Philip