I was writing on behalf of my friend. I'll forward him your advice and we'll see. He says anything more than 30* total and it pings badly from the beginning, not only at higher rpms.

I recommended him more initial (I run 22-24* in my 383) as this clears idle very well but it doesn't work with his 440 - I guess he must play more with springs'n'slots to get shorter but gentle curve.

As a last ressort he can play with gasket thickness and lowering CR but I read it may aggreviate pinging (less quench). BTW dont know how far in the hole the pistons are but he bought some forged with 4cc valve pockets.