timing
Definitely have a concern if you ran 26 degrees total and burned pistons. If your 26 degrees was accurate, you were running very lean and that's what burned the pistons up.
As far as the timing, I read an article by Smokey Yunick 40 years ago. He said the way to set your timing is to bring it up to detonation under load and power and then back it off 2 degrees. The man was a genious. That is pretty close to what the computer does on your daily driver. It is obviously much harder on a motor with a solid cam and headers, etc.
I used this method when I was a kid working in a garage in the early 70's. Some cars I would advance up to 8 degrees (at idle) higher than the manual specified. Between that and a little carb tuning. I would guarantee 2-3 MPG increase from their best MPG with my tune. In a 2 year period, I never had one come back that didn't shake my hand and thank me.
I have used that method ever since on non-computer controlled ignitions. I have gone as high as 40 degrees total on both small and big-blocks, but I would not go higher. Never burnt a piston. Higher octane, obviously you can get more timing.
If it's an automatic, the method is easy. Brake torque it in the stall/garage. jack the timing up in 2 degree intervals until it starts pinging. Back it down 1 degree at a time until no ping, and then back it down 2 degrees more for a safety margin. On a stick, you need to take it out, check for pinging at low speed and 4th gear.
Haven't raced in years, but I have a stock '69 427/390 vette. Normally run 93 octane unleaded with octane booster and lead replacement additive (not real lead). When I get a chance, I get some race gas and mix it 50/50. I can get another 3-4 degrees on timing with that and it obviously runs better, not that it runs bad with the unleaded.
Some might read this and think it's foolish. I can tell you it's worked for me for 40 years.
Good luck