OK, Slant Six Dan has reported that all 66 center links are the same, whether six or V8, and they are the same as the 64 V8 center link, which had a one inch deeper drop than the 63-64 slant six center link. 65 center links are a mixed bag, but according to him, late 65's all used the V8 center link.
I've heard similar- be it that they went to a single common center link, or that some plants were using V8 links as they ran out of /6 links... either way, check to make sure before assuming anything to be 100% true, just to be on the safe side.