All A-series rwd gearboxes are nearly exactly the same length.

Here's how you can inspect a used gearbox that's out of the car:
1. Move shifter through all the gears. Look for smooth operation, no surprises
2. Try to put some resistance on the output shaft, and turn the input shaft by hand. There should be no funny noises. It should turn smoothly
3. Inspect for any signs of damage to the front and rear splines
4. Tip the gearbox forwards and back (just a wee bit). A little gearbox oil should come out, but NO WATER. Avoid it if there is any water.