hey bro i think that the leter d stands for 70 and the eight was a 78 meanign that those were from 1978 thats how i was tought to find ford #s . iam no expert i might be wrong i have a dive block which is a 71 block and a d3ve heads 73 heads . i odnt know how good they are iam tryign to find that out it will be intresting to see how this comes out.