The interchangeable parts between the 1st gen Frontier and 1st gen Xterra are infinite. For the body and interior, imagine a line drawn along the back of the front seats and and everything forward is the same or interchageable. Engine and drivetrain is all the same and front suspension is the same. We also have like drivetrain and suspension parts with all the hardbody years(pickups and pathfinders) and the tailgate is interchangeable with the hardbody tailgate too. 3rd generation Pathfinder with the 3.3L also has like engine components and few like drivetrain parts.
Please note when I say parts are interchangeable there are a few exceptions, the biggest being that most drivetrain parts are not the same between the 4cyls and 6cyls. The difference in engine components goes without saying.
I don't know if you have seen my project but I think you would enjoy this, the Nissan Fronterra... I did an Xterra front end swap and then went with fiberglass all around.
Sent by my R2D2 using Tapatalk