I do stand against painting the interior pieces.
If he wants black, that would be the only alternative since it was not offered in black.
Maroon, Blue, Brown and Gray were the choices back then.
It can be done, but it's all in the prep work and quality of paint.
I've read ppl have had great success with SEM paint.
Could use the Gray/Black dash from the Civic Si.
90/91 Civic Si seats can be made to fit if you do a pan swap.
Use the 90/91 Si fabric on the Sedan seat frame, back and bottom.
Rear seat swap, I'm not certain on.
I do know nothing you swap in is a perfect fit.