You would only be using a shorter bolt if you decided to not re-install the A/C mount bracket. 99.44% of the time you will be replacing the long bolt due to corrosion anyway.
Keep your tap set, rust buster, degreaser and wire brush handy. You'll be using them.
You can get a foot of the good Gates/Dayco heavy duty hose at about any auto parts store, even at AutoZoo or CSK Auto. You have to ask for it by size. Ignore the usual "What model and year" question and tell them the I.D..
Use the good clamps which have the metal band which completely encircle the hose. This is NOT a job you want to repeat.
I'd suggest using the short water pump bolt and checking the system before you replace the bracket.
Never-seize and Teflon tape on the long bolt for the final install.