I looked up the first part number Drive Belt - 532140294 that you had listed and is (1/2" x 82") so is not close to the 87.5" that you have.
A manual I found has the part number 532161850 V-Belt, Drive and it's Belt Size (Outside dimension): width - 1/2", Length - 85". A83K 4LK850 which is closer to your 87.5 inch.
It is possible for a V-belt that measures 87.5 inches when it is off the machine to measure around 85 inches when it is installed and tensioned. The difference in length can be attributed to several factors:
Tension: When the belt is installed, it is stretched to fit snugly around the pulleys. This tension typically reduces the effective length of the belt by a small amount.
Belt Compression: The interaction between the belt and the pulleys can cause some compression, which can also lead to a decreased measured length when the belt is under tension.
When a V-belt is under tension, it typically becomes a slightly shorter length compared to when it is relaxed or uninstalled.
I'm not sure how you've measured the belt but you could install it and check the difference in length if it's been measured out of the mower with no tension on the V belt.
On the Deck V belt I get 88 inches which is close to your 87.5 inch length.
Someone may have used a slightly shorter belt on the Deck Belt than they should have .
The manual that I found has 95 in the lower corner so I assume 1995 and hope that is the same for your 1989 mower as the other specs were the same.
