Not enough info really. I'd probably throw it in the $9-15K range without knowing too many of the details.
The 5-lug swap. Conversion rotors and drums, or 4 wheel Sn95 cobra disk brakes? The later will drive the value up.
Quality of the conversion? Hacked up wiring harnesses? Or donor car with all the correct wiring installed? Any shortcuts taken or was the swap done as close to OE spec as possible?
The big one. Rust, body damage, paint. A paintjob on these cars is $5-10K easy. If the car's paint is in great shape, that will add value. If it needs a paint job, then closer to the lower end.
The black interior. Original? Or a pieced together swap/painted interior?