I wouldn't do that to your frontier,but I would sell it,buy a nice s10 with a blown motor cheap and do this-
Cummins 4BT & Diesel Conversions Forums - Powered by vBulletin
The Cummins 4BT is a 4 cylinder HD Cummins diesel.It uses a standard chevy bellhousing,so it's a easier swap into any GM or Chevy light truck. The motors are bullet proof and can make 500 hp easy.......and still deliver 30m +mpg.
BTW,you would be hard pressed to ever recover the cost of converting your present truck .