..There are many combinations of heads/deck height and piston dish volumes. If a 77 short block is used with 72 heads you get a cr of 8.8 and with 73 heads you get 9.3. Just about right. For long block ( that includes hesds) 69-72 would be the choice if you could be sure that's what your getting from a rebuilder. Next choice for best power would be a 78 long block at 135 hp and 8.4 cr. These engines have heads with different rocker arm design but still ok for you use.