There is a retaining ball I do believe under the cams. It just pulls straight up and off.
The Kenmore top hat cams come in several colors. Red, grey, orange, green. Shop GW has some on auction right now. Here is a pic of the Kenmore 158-17560 I sold last year:
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There are over 50 different single and double cams available for this type of cam machine. They came in standard for the machine set as you can see in the pic and a deluxe set with 30 cams you could buy on the side. Different series Kenmores used different color cams, but they are all the same regardless of the color.
That is a great machine. Although I sold my 158-17560 I kept the 158-17570. With the right attachments and accessories they'll do everything from chain stitches to monograms.
Joe