You have to run the 69 351 heads. Later ones used the toilet 302 emissions heads with the smaller valves and larger combustion chambers. Using the 351 heads requires either spacer washers for the 7/16" head bolts or drill and tap the block for 1/2" bolts.
That is incorrect. 69 and 70 351 Windsor heads had the smaller chambers and 1.84 intake valves and larger ports. We used head studs with hardened washers, no problem. Not sure when the 351W went to small ports and valves, nor did I care.