Adding a turbo can get quite expensive. You might have to put in different pistons and a different camshaft, let alone exhaust and intake manifolds, and maybe a whole lot more. A "smoke" turbo might be more doable, but would be of minimal boost.
If you want a turo'd engine it would be cheaper buy a turo'd engine and do a swap, though that would end up costing quite a bit too.
On my non-turbo Cat 3208 I thought about adding one, and with that engine the only viable way is to buy a turbo'd 3208. I found some excellent candidate engines on auction sites that were reasonable. But as my bus is in effect a cabin on wheels I gave up on that rabbit hole. No crossing the Rockies, I guess.