34 year old balances. Springs and string long gone.

I have single hung windows. 28 inch long balances, half inch wide. Stamped 2 7 3 0 (backward C) BSI. There have never been take out clips. See photos of window frame. It appears mine operates a little different from your video I watched. I need this black piece also that attaches to the top corner of the window. One side is broken off. I will also need some take out clips that I can use to put into the two small slots so I can remove the good windows for cleaning and or further inspection. The only reason these came out is I yanked the spring and cord out long ago when the windows got jammed up. The string was getting tangled in the channel. I looked at the post from John from Aliso Viejo from January that my balances look identical. I too am selling my house and I want to repair these windows. 3 out of 8 need replacement balances. Can you help?!!

Hi. I was able to remedy the side clip issue to remove a working window by putting a machine screw in the side clip hole to prevent the balances from going to the top. It worked! I was then able to remove the working balances that had the spring and string pulley system intact so you could see the type of balance I have. 

So the black piece I mentioned in the prior post I have learned this is called a top sash guide. I unscrewed a good one so you can see what I have. It's in the photo along with the photos of the spring and string internal workings, also showing the clasp that hooks into the side of the sash. 

I also have a couple other photos added that show a good balance still attached via the hook into the side of the sash. I hope this additional info helps. I think to make an impact I should replace all balances in my windows. After all they are 34 years old. I would probably want to order a set of removable take out clips so I don't have to use the screws to hold the balance. 

And I would need 4 top sash guides just to make sure I have more broken ones. And I would order 16 balances for all my windows. Can you provide the SKU or item number so I can order the appropriate items. Thanks