I've been working on putting an engine that doesn't have as many miles into my truck because the one that was in it crapped out and I need some tips and pointers. I also need to do this cost efficiently.

1. My first problem is the rust holes in the firewall that I have clue how to fix.

2. What are things that I should do or check on the engine since it is a used engine that has 80,000 miles on it.

3. One injector on the newer engine is tore up should I buy a new one or pull one off of my old engine.

I will probably have more questions later, any help is appreciated thanks!