I wouldn't have a problem doing that - I did that twice with one set of bottom parts "back in the day' of the 312 Ford 'Y' block. Just do a good block inspection and use good assembly practices - clean as well as measure. The only place you could get in trouble is to use a 28 in oz set of bottom parts from the '68 with a 50 in oz block which happened in '81 or '82.