Maximum lift with stock J heads

If someone gives you an across the board answer, that's inaccurate. This is how it is. If you want to know an exact number, you have to measure retainer to guide clearance on what you have. I've seen some go as far as .520 lift and as little as .470. That's because Chrysler was not consistent with the heights of the guides. They're going to be different head to head. So measure.
Now you got me akin to go out to the shop and check my 587's against my J's...