400 HO did not arrive until the 1968 model year. The HO for 67 was a 67 326 HO. Here is a list of 400 WQ blocks. Check your block casting to identify which year.
Year Engine HP Engine code Trans CR Cam Head Code BBL Carb No. Misc 1967 400 325 HP WQ M 10.75 744 670 1-4 7037277 RA A.I.R. Block Casting # 9786133 1968 400 335 HP WQ M 10.75 068 16 1-4 7028271 HO Block Casting # 9790071 1969 400 335 HP WQ M 10.75 068 48 1-4 7028273/7029273 RA III Block Casting # 9790071/9792506
