Thats a frame I built, a Huffy Reatta. Engine fit well but was high enough to need a fuel pump to feed reliably.
Fuel pump was no issue to install. You can see the pump under the seat.
I see exactly why you needed that fuel pump.
You will notice that the pink bike pictured in post before you is using a standard tank that is also raised higher than yours allowing for gravity feed.
Yours is on a different type of rear rack that is mounted lower as well as using a slim tank that also sits lower making it necessary to have a fuel pump.
Your engine is not sitting any higher than the one on the pink bike, but your rear rack and tank are definitely lower than the pink one.