driveshaft angle ?

I have a 73 scamp with a 833 4speed and a gear vendor overdrive I'm going to get the driveshaft shortened I need to know what the driveshaft angle should be. I bought the inclinometer tool to do the job. just need to know what to set the angle at.
How much of an interference to the floorboards will the gear vendor create? Are you concerned about cutting up the floor to get it in, or wondering if you can tilt the engine/ trans combo back and have it fit without cutting up the floor?