A 76 TA w/ a 455 will have an engine ID no. of 500813 cast in raised numbers behind the no.8 cylinder, just over the oil pump filter bracket. If you know it's a 455 for sure ('455' cast on the outside of the block outside of the no.1 cylinder, '55' cast in raised numbers in the lifter valley) and your numbers don't match, then your block has been replaced.
Geno