If you're asking that question, you can't do it.
Either spend a ton of money having an auto fabrication shop doing all the work for you, or change your mind on doing it.
If none of those options are suitable for you, then spend hours and hours learning to fabricate and pour over other peoples build threads until you can find enough similarity in swapping some engine into a Subaru, and swapping an RB engine into something that normally doesn't have one.