The 700r4 uses the TV cable for shifting and the computer for the LockUp Torque Converter. When switching to a carb, make sure you get the TV cable hooked up at the right angle and adjusted properly. You could run it without a computer but it wont go into lockup mode, which could lead to pre-mature failure of the transmission.
You can make you're own lockup switch by following the links irish posted, or there are some companies like TCI and B&M that make kits you can install.