1'st of all, I agree with Spud. 38-40° lead with non-raised runner 23° SBC, it seams it's all about combution camber design. Non RR heads at least 36°, raised runner 23° is happy at 29-32°, and 14° RR heads like 28-30°. I run that timing racing under 3500 DA. When we raced Salt Lake City [ 4400'] and 7000 DA, I put another 4° in her. Again this is burning alky, gas and nitro is another game.
I use a Snap-On cyclinder leak down tester, any good tester will work and of course Spud's custom tester will work good. In my experience 29% is way too fat. I set mine at 18% and any time you change the barrel valve you will have to adjust the idle set screws. one reason I like 18% is it helps get the engine up to the temp I want, 180-190° as we are getting into the staging lights, on my all iron, water in the heads and block, SBC. Alky runs better at higher temps. And of course no problems with milking the oil.
I hope this helps.
Jon 805-444-4489