1967 they went from the earlier squish-band head with slightly domed pistons to the later hemi-heads and high top pistons,so the earlier heads won't work on the later engines unless you fit the relevant pistons too. They changed in more subtle ways (pushrod tubes, rocker boxes etc) too over the years but you can get around those problems easy enough.
By the way, there were no T100SS' in 1968 as they stopped in 1966, so maybe you mean the entry-level T100S model?
