You can only remove individual sheets without processing, it is type 55. You cannot remove the sheets individually from the pack film holders unless you take it in the darkroom and then you would probably screw up several other sheets.
The 405 holder does fit in spring back cameras such as Sinar's and Horeseman's. It looks like it is way to thick but it works just fine. I used to use the 405 "pack film" polaroid before most of the catalog work went digital.
Both the 545 and 405 are for 4x5 cameras. The 545 uses individual sheets such as Type 55. The 405 holder uses pack film instead of sheets. The 405 Polaroid produces a slightly larger image area than the 545. An example of the type of Polaroid used in the 405 holder is Type 559, the old style emulsion of color Polaroid. I just looked at B&H's and Calumets web site and I did not see Type 555. That is what the designation would be for pack film black and white P/N 4x5 Polaroid. I'm pretty sure they used to make it, I think a friend of mine in college in the late '80's and early '90's used it.
As far as the 405 holder is concerned, I consider it the black sheep of the Polaroid family. Most people prefer the 545 holder even though you get a larger image size on the 405.