The machines built before October 31, 2000 did not have the height adjustment knob. Go to the parts look up and it will show that. I think the manual you need is 770-10520.
All my early ones have the "Shaft Drive " decal like yours. Here is the one on my 3205. It also does not have the height adjustment knob.
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The rear covers are steel on the aluminum rears. Here is a pic of an aluminum rear with the differential lock like the one that should be in your machine.
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Cub Cadet made the aluminum rears. The cast iron rears that I have had were stamped "Made in China".
Most of the 3000 series all had 24x10.5x12 tires. Some of the later ones had 23x9.5x12 tires. Nobody makes 24x10.5x12 tires now. You will need to replace them with 23x10.5x12 when the time comes.