I think they set the anlges of the card guides? it's been a couple years since I messed with one, but I recall they did something odd like that.
I would think they are for carbon ribbon, if I am looking at the right parts.
If you are talking about the two large spool holders at the front, those are indeed for a carbon ribbon to be fed into.
The "two spools" you're referring to---are they the largish ones closest to the front with the holes in the flanges? If so they are for a carbon ribbon. The green diagram on the left one shows the threading path, though I can't tell from here which is the supply and which the take-up spool. It looks like the ribbon color selector switch above the backspace key has four positions. probably Carbon, Black, Stencil, and Red, reading left to right. HTH == Michael Höhne