I am curious about the string spacing. It looks like you may be going with the Hipshot, which could make the point moot if it has adjustable string spacing...
Curious what makes you interested it 20mm? I have three basses with J necks. Two have 19mm and the third has 18. If pressed I would probably say my hand likes the 18 best, but it's not really something I notice. I don't see much of an advantage to having the outer strings closer to the edge of the fingerboard. Of course that could be my ham-handed tendency to push or pull outer strings off the fingerboard with my left hand when not paying attention.
Fender American Standards seem to use the same high mass bridge, and I thought that was true for other years as well. My 70s Fender P uses 19mm spacing. Did Fender use wider spacing on J basses at some point?