Thanks Dave, since I have already discussed this with contractor and his official reply was the API610 para. 5.5.5 and the F.1.2 that I sent earlier.

That's why I question how I can challenge him that the API610 Annex F is not appropriate.

Lately we decided that since Annex F is conditional on purchaser acceptance. We shall not accept it's use because Annex F might increase deviation of internals by more than 50% and the client is already suffering from pump problems due to internals deviations and pump seizure.