7 1/4 to 8 3/4

I think he's trying g to BUY the right shaft. You won't find one. Take your shaft to a driveshaft shop and have it made into what you can use.
(The chart says your shaft needs to be 2.25" shorter.)

As said above, look at column C. It shows axle centerline to yoke c3nterline, for both a 7 1/4, and an 8 3/4. 2.26, ten thousandths away from 2 1/4.
Plus, you may have to have the shaft modified to fit the u-joint required for the 8 3/4.
So, follow the advice others have given you, take your shaft to a driveshaft shop, and get it made right!