I'm not a suspension expert, I deal with motors and drivetrains. BUT, as I do have a Engineering background, please do as Francis said, washers are needed on the sides. The lateral thrust needed to pop a heim out isn't much, especially if they are the nylon/propylene surround on the spherical ball. Plastic compresses. The old style with the crimped capture of the spherical ball was much better and could take alot more pressure (heavy duty). They had to be lubed though, hence the plastic (light duty).
Also, the Nylocs are a wise choice to keep nuts from backing off. This is just my 2 cents here, but I like to use 'crimp nuts', the ones that either have the edge crimped slightly or the crimped middle area.
After many test fits to make sure all is as it should be, I do final assembly with the crimp nuts going on, and a touch of loctite to help assure holding.
The loctite actually lubes the threads slightly to ease the installation of the nuts, and just a touch stays in the threads for additional holding power. The majority stays at the outter threads, assuring that things will stay put....
The metal to metal contact is a good thing, in the fastener world....