That 29 degrees number was just what I have the best power and torque with on the dyno. Every combo is different what is good for mine may not be good for yours. On the dyno we usually tune for max power, which is good if you run the car at max power, mostly race, but most of us use our cars for purposes other than race. You also have to consider what your lower rpm and cruise rpm will be like with a lower setting. When I first installed and ran mine I set the timing to 29 total, that only gave me 8-9 initial. My car ran roughly and hot at idle with the low advance. I didn't know at the time my vacuum advance wasn't working. After repairing the vacuum advance I got a smoother and cooler idle but a slight ping on partial throttle pulls, especially up hill. At WOT it was fine as the vacuum advance goes to zero with the throttle plates wide open but I was getting too much advance in some instances. I had the timing curve I wanted but needed to lose the advance at part throttle yet still have more advance at idle and low rpm. That's why I welded the slots on the low advance side instead of stopping the advance on the high side. I still get the curve I want up to 3200-3400 when the mechanical is all in. The joys [pain] of having a modified engine. Normally one would set the initial from 10-14 and the mechanical to 32-36, with the vacuum operating one would have around fifty at cruise for a nice cool and economical run.
Is your 400 stroked and bored to 463 cid now or is that a planned build?
Your 62 heads will have a small chamber, 72-75 cc, it may not be the timing that is giving you the detonation but the compression. A lot of factors to consider when facing detonation, grade and quality of fuel, quench, heat dissipation, static and dynamic compression ratio, timing, driving style, weight, gearing, cooling, etc.
You say you want high torque from your engine. That's a rather large camshaft, good for high rpm horsepower but you'd most likely get more torque at lower rpm with a smaller cam. I don't know how the 62s flow but you'd have to flow fairly well to use that cam.
