If the car in question has the correct engine, you might find that it can be repaired for less than a V8 conversion.
As for the desirability of a 3.0 turbo, a nice one is worth $10 or $15K more than even the nicest V8 conversion.
The other option of putting a normally aspirated engine in this chassis as a driver it would make a very nice car.
Let's do the math.
Fix the turbo $10K maybe for engine repair ??
3.0 turbo with rebuilt engine = $18K to $25K
V8 conversion $5k to $10K
3.0 turbo with V8 conversion $10 to $12K ??
Who knows but it seems like a no brainer.
BTW: If you choose to change the engine I am a player for the 3.0 turbo engine.