IMO,
If the PHS docs say it's an HO car and you can prove with reasonable evidence that it is a 400HO then it's a 400HO. However, 400HO cars that are missing one or many of the major components that come with a 400HO are with progressively less with each missing part.

Here is a list of relevant 400HO parts (might be missing some):
400HO engine (serial no. verification against PHS doc)
Chrome air cleaner top, valve covers, oil filler cap
carb, distributor, intake, LBM's, alternator
transmission (verified no. to PHS docs)
rear end (date code and axle code)
HEADS! They are 16's (only come on a 68 400HO)

With that said, I believe Harold has a 400HO car with a very close engine. The exact same car with the correct engine should get better $$'s, but they would also have be restored with the same care and attn to detail that Harold has done with his car. It may be harder to find many Firebirds in better restored condition.

And besides...Harold is a 2nd amendment dude ... don't [censored] with him! ... lol