Not counting the turbocharger itself, I would simply extrapolate. If the NA went 100K before conversion, it used one-half its life. If you turbo it, it has one-half a life left, but it’s now a turbo life. One-half a turbo life is 50K. So you should plan to rebuild the engine at 150K, and you still have another 50K to go on the turbocharger itself.
But, you would need to put on a new thicker gasket in order to drop the compression to 8.4:1, and while you had the head off you might as well do a complete top-end job. So, if your bearings hold up, you might push the car well past the theoretical 50K.
How heavy is your right foot?
We would all like our cars to run forever, but it ain't gonna happen. My mom actually put 350K miles on one engine in a Toyota Station Wagon. Lots of highway cruising at 55.
