Gears & Axles - 12 bolt DS with a 9inch rear

I got 9 inch in my car and discovered it has a 12 bolt DS in it. Its 1 inch to short, there is a drivetrain shake at about 90mph and higher. I'm ordering a new shaft tomorrow. I've been working on this car for 2 weeks getting it ready to race again.

Will I damage the car racing it like this?
Thanks
Jay

I talked to Bob, he said it should be fine like that but it might be causing my shaking. I ordered a new one yesterday hoping the shaking stops
Jay