correcting pinion angle

[1969burb]

Hi all! I was wondering if anyone could let me know how much correction is necessary for a 5.5 inch rear drop. I bought a cheap angle finder but my understanding is the vehicle needs to be level and have full weight on its suspension to check the current angles. theres not too much room to get under it w/o a lift. just wondering if anyone had a personal experience with this type of situation. also where is a good place to buy the angle shims for our trucks? (burbs) I have a noticeable vibration at 35-45 mph and the driveshafts have been balanced and new carrier bearing and u joints are installed, so I'm assuming it must be an angle issue. thanks for the help, steve