The factory does not use lock nuts. Just make sure the adjusters are fairly tight, so they don't move on their own. The adjusters are supposed to be an interference fit.
Charlie is the man here so I'll defer to him. But isn't 3-4 threads showing below the rocker about normal?
The pushrods appear to be about the right length.
Try it again without the locknuts.
The Chrysler stamped rocker arms were somewhat of an engineering marvel when introduced. The adjusters are an interference fit when everything is right. It is probably not possible that your new rockers are brand new reproductions but rather "renanufactured" originals. Cleaned and reground pads. (Another variation contributing to clearance stack up by the way). So maybe the rocker vendor is covering their butt by providing locknuts to make up for a worn out interference fit. Leave the nuts off for now and check for torque resistance.
With so many unknowns in that engine, you may need a custom pushrod length afterall.
