Yes 18 would be his total max timing at max boost, which i believe is actually the max timing LA3s had with the premium fuel switch mode on. Kev your funny cuz you were practically running race gas :p
Jed, just remember when you get on the dyno, now that you have extra time to utilize, try to have your afr completely dialed in to where you will not need to worry about making any changes to it on the dyno, and also that boost is as consistant and stable as you can get it. There will definitely be a load difference between what boost your seeing on the street vs what the dyno will be, so be prepared to possibly see a slight boost variation just in case you need to make a last minute adjustment
Also one thing to keep in mind, when i dyno'd for the first time using 93octane, i was only making 260ish rwhp and under 300 tq on 24-25 psi and avg'ing between 20-21* timing and i couldnt tell if it was the dyno or the timing but it felt extremely sluggish in accelleration. I made about 3-4 passes like this and the results were all about the same.
Leaving boost and afr alone, i dropped timing down to 18* max and gained ~30 hp & tq so i had defintely found the area of my timing threshold, but couldnt play anymore because i was at my pull limit for the dyno day unfortunately
For the sake of safety since i know you like to blow headgaskets
i would defintely suggest making your first pull with 16* max timing, and if it seems to be pulling clean, add in 2* back up to 18 to compare. If there is very little gain between the two pulls than obviously 16 or 17* may be your safety margin if not lower but i honestly think somewhere between 16-18 will be your sweet spot
My number for you is going to be on an optimistic side of 36x hp and 42x tq, my mustang dyno guess would be 34x hp & 39x tq
Goodluck man
