Any recommendations for a a high quality polish for black?
A good product for black or any single stage or clear coated car comes down to doing a Test Spot. Doing a Test Spot will/should tell you if the paint is on the soft side of the soft/hard spectrum or on the hard side of the soft/hard spectrum.
One product I can strongly recommend for any soft paint is to finish with the Dr. Beasley's SNP 45 - it excels at finishing out perfect on soft surfaces, including clear plastics.
Finished out the clear plastic window on this Amphicar using NSP 45
1964 Amphicar – Paintwork, Glass & Plastic Correction
I've detailed this GTO twice now, the second time because the shop where it was at for some repairs, wiped it down with a tatty towel and re-instilled zillions of swirls and scratches. The paint on this car is a single stage urethane and super soft paint. I finished this out with the Dr. Beasley's NSP 45 - other big name brands all left micro-marring.
Removing Windshield Swirls, Scratches & Wiper Marks on a ’69 GTO with Dr. Beasley’s NSP GL by Mike Phillips
No pictures, but my long-time friend Shawn who owns and operates a car wash in Hollywood, Florida, drive from there to here to pick up some NSP 45 to finish out a black Chevy Tahoe with soft paint. He ran into the same problem, that is, even the big name brands he normally uses was leaving micro-marring.
I show using it on the clear, flexible back window on the 1965 Oldsmobile 442
Just an option to consider after you find out if the paint is hard or soft.
Mike