I would suggest going ahead & getting it (the tires) up on blocks & leveled side to side and front to rear cuz we need a tight ship on this one & yes Dayclona is right that the rake is unimportant since if for instance it was way tilted up front to rear & the trans was down say 10 from horizontle and the shaft was down 12 from H then the shaft is 2 deg down cuz it is where the shaft (ujoint) is in relation to the trans which is what we're after. If the trans was down 10 and the shaft was only down 8 then the ujoint would be 2 deg up which means at the other end we'd want the pinion up 10 & with the shaft only 8 up, the shaft (ujoint) is 2 down in relation to the pinion. It's all about the angle of the ujoints to the shaft. (1) need at least 1-2 deg away from a straight line on each end (2) but not too much of an angle (or the ujoint will bind if real excessive or just wear out prematurely if moderately excessive) (3) need angles equal and parallel but in different planes (ideally), 1 up/1 down (plus the slight extra pinion down depending on intended app). I'd say the vibration is either (1) driveshaft balance (2) not enough yoke engagement into the trans (3) ujoint angles. Keep us posted. EDIT another thing to keep in mind is an imaginary driveshaft suspended in air with the left (higher) end at 10 o'clock and the right (lower) end at 4 o'clock the left end is so many degrees up (from horizontle) and the right end is so many degrees down (from horizontle) with the number on each end being the same with the car leveled side to side and front to rear but it is a good idea to check the shaft angles at each end before you pull it to then check the trans/pinion angles