In another thread you asked this question:
The black hawk came with a old briggs fun power. Should I keep it? Would it be worth fixing? There is no way it is original engine
What makes you say there's no way it is the original engine?
By the very nature that it is a Briggs
Fun Power engine (designed for go karts and minibikes), it came with your kart and that Brister's has a long habit of using red Briggs engines (Fun Power or not) on its karts, I have to conclude that this points to a very high probability that it is the original engine.
Yes, you should keep it and fix it up if it is feasible to do so... [but that's another rabbit hole]. If I were you I would have assessed the engine before buying a new one but I know how to fix them and you probably didn't want another rabbit hole to go down. There is a lot to be said for keeping things original.....
There's a serial number code stamped into the red blower shroud that includes a manufacture date. IF the engine is original to the kart, the date code from the engine can pinpoint the date the kart was manufactured, or be very close to it.