Shift kits are just kits that put higher amounts of pressure through your valve body making the vehicle shift more "positive" so to speak. The shifting will be harsh when cruising, kind of like a kick in the pants and it might even let off a little churp. Your stall converter size should be coming in when your power comes in, so lets say your cars power band is from 3 - 7500. Your converter would need to be 2800 - 3200 or thereabouts.
It would still be streetable, but will chew more juice because of a stall converter. You are still able to drive the car in D unless you have a semi manualised or a fully manualised valve body, then you'll need to manually shift from 1 2 3 D or whatever pattern your car has.
As Ben stated, a decent sized trans cooler is a MUST when it comes to stall converters and stuff.