68-69 383hp had positive deck height. Actually I thought the 70 and 71 383 hp engines did also but maybe not. 68-69 hp used the 906 heads. I don't remember if the 70 and 71 did or not.
I'm pretty sure 68 was the only year 383 Magnum was zero or positive deck.
I pulled apart several 68 383's and the pistons varied from slightly under zero to .005 out of the hole.
