The 1967 Cadillac is much different than the 1968 in consideration that the 67 has a 429 engine w/adj mount for compressor, and the 1968 Cadillac has the 472 with intake solid mount compressor with ps as idler pulley and it also has an air pump (unlike a 67).
Use the 1967 shop manual. You probably could go on e-bay and look at an under-hood picture of a 1967 Cadillac and figure it out. The belt for the ac is difficult to get installed (due to small adjustment - has to be fairly tight), and unfortunately you have to be careful and install a very high quality belt or it will slip and make a noise.