Sounds like quite the ordeal, stinks that it happened. But I think you’ve answered your own question, and it wasn’t the oil’s fault, at least not directly. Your last sentence should always cause a hard stop in any project, especially when dealing with a fine piece of machinery like you’ve assembled so far.
An old saying (which is as much a reminder to myself as anything): If you can afford to fix it, you could have afforded to do it right the first time. Looks like you got a handle on things; remember that moving forward til everything is “right” and you’ll be much happier.
Got any pics of the engine/car?