That sentence is correct; the register would suit a fairly formal description of an historic event. ‘I says’ would never be correct - if you see it written in fiction it would suggest the speaker is poorly educated. ‘Says I’ is not grammatically correct but is sometimes used in historical fiction when the speaker refers to themselves in the third person, eg. ‘The gold is mine, says I’. It would sound out of place these days. Better to begin the sentence with ‘I say’, in my opinion.

It was A heroic deception. (H is pronounced, so use A) Is there any situation in which "says I" or "I says" can be acceptable or right? Says I -reminds me of old, historic English I says- It is said jokingly or as child speak.