Rough timing recommendations for 2nd stage

552ci 13:1, P-51's, Victor Jr, 1250 carb, solid roller @ about 760 lift, 116 octane and NGK 10's. I swapped in a 2 stage plate where as I used to have only a single. Car holds hitting it with a 175hp shot upon release of t brake and pulling 9* timing from 30 after careful tuning & plug reading. Planning to add a 125hp second stage a little bit out. How much more timing should I pull? I was guestimating 6* more to be safe and tune from there. ???
15* total sound like a safe starting place for 300hp nos or go even further south? I'd rather start safe and slow than burn my sh!T down.

i pull roughly 13.4* from a 27* base for my first stage which is around a 300, id say your in the ballpark.... pull an extra degree and sneak up on it to be safe imo

Thanks. Will do.