replacement channel balances

I need to replace both channel balances on window since it will not stay up. The only number on them is 283000A J. This is no other identification such as manufacturer. They are both 29 inches in lenght 1/2 inches wide and 5/8 inches deep. This is not tilt window (top outside window fixed). Slider window which these are from is removed by pulling out both clips on inside top of frame then sliding window up over clips. Attaced are 1 photo of top and 2 of bottom edges (note corner of piece is broken).

THANKS. I agree with your choice for top which is identical as show in photo, but the bottom piece appears to be slightly different since it does not extend up behind the frame as shown in first photo posted or do you think that it orginally did and broke off (it only appears that corner is missing to me). Maybe I should examine another window where the balance is still operational to see design?? Any thoughts or suggestions?

attached are additional photos of bottom piece from another undamaged unit. It appears to be similar to the part you are recommending. Size is identical outter edge appears to be square while your part is slightly rounded. Does this matter or is than an alternative part?