Where does the center stand spring attach to on the chassis?

this depends on design of side stand - usually the easiest way is to remove the side stand pivot bolt remove side stand from channel., attach spring to both ends. pull side stand into pivot hole and reinstall bolt. there is less tension and easier to install if you orient side stand in retracted position..

The PTO cable will come out the chassis straight down from the engagement lever on the right side of the dash panel. Will be fastened to the frame on the right side in front of the rear wheel with a zip tie. Loop over the brake rod and attach to the deck on a tab at the rear center of the deck. A hair pin will secure it there. The inner cable continues from there under the belt and the spring hooks into the engagement bracket. There may be two hole for the spring to hook into. They are marked 38 or 42.

place the trolley jack under the front cross member . (The big bit that connects the side frames under the sump). Lift as high as possible and place the jack stands under the chassis ( moulded rails ) where the sub-frame meets . Then place the trolley jack under the rear diff and lift as high as possible Place the jack stands under the chassis at the front of the springs or track rods By using these positions you will have the cabin securely jacked up with all the wheels free to remove or to work on. Before going under try rocking the vehicle hard to ensure that it will not move off the stands.

Check the counterweight spring attached to the lower portion of the tub at the rear going to the rail on the chassis

Have a friend hold bike up for you with the kickstand in,attach spring to kicks stand, and with a pair of needlenose pliers stretch the spring to attach to the loop on the frame

After the bowl has been frozen you attach it to the base. Then you take the part your asking about and attach it where you would put a beater or whip. The trick is to make it spin and the notched part stay in the "center of the circle". You don't use the top front of the mixer. I had to practice without the bowl and beater bar to make sure I had it right.

you need a helper or a motorcycle stand so you can then remove center stand

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Take the bolt out of the kickstand, attach the spring, then use the kick stand for leverage to stretch the spring, and re-install the bolt...

Yes , it may require some light lubricating at around the stand but first you will need to clean up throughly around the stand fittings better to use WD40 and thn some mineral oil as lubricant.
Not bad too to check the spring of its tension!
Hope this helps!