Are the gunsmith kits available from Pachmyr, Forster, or Brownell's worth the cost? Any diffference in the quality of the screws?

Forester is kind of the high water mark in my experience

The screw kits from Brownells are first class. They are of good quality. They stand behind them like everything they sell. If you're not satisfied, just send them back.

I was surpised to learn that Forester's screws are made of leaded stock! But they heat treat to the point I've only had one slotted screw fail when I really put the "crunch" on it.

I feel they are worth the extra cost.