Poly bushings should be a pretty tight fit into the outer shells. They also need to be greased with poly grease, especially if you’re not using greaseable pivot pins. They shouldn’t need a press to install, but if they’re loose you’ll need to replace the outer shells because they need to be a tight slip fit to avoid slop and premature wear.
If you have Poly or Delrin LCA bushings the pivots/pins don’t need to be torqued at ride height. Those bushings rotate on the pivot/pin, so it doesn’t matter where they get torqued.
As far as keeping the pivot/pin from spinning, I use an impact. But a lot of the aftermarket pivots come with a nylock nut, so that doesn’t always work. The factory used a crush nut. So in those cases sometimes you have to grab the pivot by the shoulder from the LCA side to keep it from spinning. If the suspension isn’t fully assembled you can slide the LCA back to get the room to grab the shoulder, don’t damage the surface the bushing rides on. With Delrin or poly bushings you can just install the pivots/pins by themselves and torque them like that, then install the LCA if you want.
Another option would be to just use a lock washer and a standard, non-locking nut. With the final torque on those nuts having them loosen up is pretty unlikely. You could use Loctite too. That way you’d be able to spin the nut on with an impact and when it hits the lock washer it should grab and not spin the pivot.