I remember having issues with a set of stock 1965 aluminum K heads not torquing down well, some of the head bolt bosses wanted to collapse a little failing to hold at the stock lengths in those heads.
That motor was the original A990 motor out of a 1965 Dodge or Plymouth according to the owner, he had a set of the proper Holley cars prep by John Bauman as well as a set of the original spare stock heads and exhaust system