Can't get Pro Parts headers to fit.

Yes, some of your issues may be solved having the engine in the right place, I think the first pic didn't have the mounts in (iirc), so I was trying to get you to stop cutting and start measuring, lol.
The headers are made for stock engine offset, I would imagine?
Keep at it, you will get it.
Cheers

@roccodart440 . lol