Hello everyone!, I’m relatively new to Hondas but have worked on quite a few cars (mostly American)

Anyways here is my situation. My neighbor has a 06 civic si that about three years ago had an oil change done and the shop didn’t put any oil back in. She drove the car to and from work (1 hour one way) with no oil. Obviously the engine got wrecked from this. She claimed it was seized. She asked if my friend and I could replace the motor and she would split the profits with us.

my friend and I finally got the time to go check the car out today and it’s in good shape. Just needs a bath and a good vacuum. We gave the car some juice with jumper cables to see if the electronics would still come up. We got full power for everything. I tried to turn the car over and the engine actually cranked over! Obviously I didn’t keep doing for fear of there still being no oil and don’t want to further damage the engine.

So with that all said should we try:
—Buy a used K20z3 and replace it with the damaged engine? Couldn’t find any in my area but found quite a few K20a(s)
— Buy a K20a? Will it be a direct fit ?
— Rebuild the K20z3 that is in the car already?

thank you for reading this long post but any help will be greatly appreciated!!