Well according to the info I have;
Centerline of Axle Shaft to Centerline of Rear Universal Joint
7.25 is 10.09"
8.25 is 11.69"
8.75 is 12.35"
Assuming your trans is not being changed then yes your drivshaft is too long now by 1.6"! But I wouldnt go by this, I would actually measure the new length with wheels on the ground.