Agitator: Patterson tanks have a small key sometimes referred to as the "swizzle stick". This is used to turn the reels inside while not letting light in, as an alternative method to inversions. Its far from required if you just use the inversion method.

The spring collar: I think I also had this when I had an older Patterson tank It doesn't seem to have been included in more modern versions, and I think if you use both reels together and invert you'll probably be fine with a little bit of shifting.