Cometics won't leak.
Items that cause detonation : heat - both stored in the head, block, piston and spark plug, and high intake temps; poor squish most commonly caused by too much quench or lack of quench pad; too much timing for chamber efficiency; too much timing for fuel and compression; too lean; excessive coolant temp, and much more including combinations of any of these.
You are unlikely to detonate it if running at the track due to lack of heat soak and large amount of air flow due to WOT driving if you have the AFR in the 11.0-11.8:1 range. Detonation happens at slower speeds, short blasts with heavy heat soak (street driving red light racing).
A couple of things to keep in mind - you could run 15:1 with 94 octane in a race only build without issue if you can tune. The difference between 12:1 and 11:1 won't be 10-20hp with everything else the same, but will be much more tolerant of the items I mentioned above. Regarding quench, an LS is not affected by too much quench near as much as most old school stuff due to the chamber design, but there is a limit. I would recommend against much more than .065" if street driving in the hot days of summer will take place.