Ignition timing for NOS

Here is what I would do.

Head out to the track one night and pull the timing back 4 degrees. Make a pass. Pull some plugs and make sure you don't have any detonation, no silver flecks on the spark plug insulator. And when you pull the plugs pull of the track as soon as possible and do it on the side of return road. Do not drive back to the pits cause the added run time can obscure the signs of detonation. Bump the timing up a degree and repeat. If you get any silver flecks or have any detonation then back it down a degree and you should be able to leave it there.

One other thing that you could do is get an MSD ignition or similar with the additional timing retard. Then you can back the timing off with the turn of a know when you need to and then turn it back to your NA setting. This is what I am going to do when I swap my nitrous setup off my 93 onto my 88.