Yes as Mike said the 58 doesn't fluid couple well at all. Basically unless it's locked it's very inefficient. The 78 still gives you some rpm to help spool your turbo but puts the power to ground even unlocked.
Interesting as with everything and everyone results may vary but I sure do have a lot of great running non smoky fully built trucks out there that Kory has tuned.
I stay about 3 weeks out lately it's a month. The converter would work great even with a stock turbo. Feel free to call me and we can go over options for everything.