With the 400 and 62 heads, you have no detonation at that timing? Are the #62 heads stock volume?

I have a similar setup, stock '69 400 with stock intake, carb, 067 cam, #62 heads, but stock exhaust manifolds. I get significant detonation on anything over 24 degrees total timing or 9 degrees initial timing if I run anything less than 100 octane R+M/2.

I will be rebuilding in the spring, just curious as to why two similar configurations act so differently. Any idea what the lift and duration are on your Crane?