CAN THE PINION ANGLE CHANGE ?

Ok so now put the D-shaft back on with the correct straps and in the right sized yokes with a tightened to spec pinion nut. Make sure the shaft is not too short. It should be set about all the way into the tail and then back-out 1inch as a working length. You should have to push it back into the tail to fit it to the rear yoke, and then pull it into the saddles. Make sure the U-joints swivel freely, and smoothly.Finally,grab the D-shaft at the front U-joint and push it up,down, and sideways. I don't have a spec for how much is too much, but I suspect .080 at the U-joint cups is too much.
Then verify the vibration is still there. Then jack the car up, and onto axle stands. And retest. If vibration persists, remove the wheels and tires and retest. If it persists remove the drums . Do not hit brake the brakes with the drums off.
At this point you're down to axles, and pinion angle. So first check/adjust the axle endplay, and retest. Axles are seldom bent and you said it was fine in the other car.
So that leaves the pinion angle.
The driveshaft has to run at a non-zero angle at both ends to keep the needles from pounding into the crosspin.This also keeps the grease moving around. Usually the shaft goes down to the diff from the trans and back up to the diff at the other end, this is called nose-down at the back.The angles at each end should be equal and opposite in direction, when under full power, but not less than zero at the back, that is to say not nose-up relative to the driveshaft..
To achieve this, the pinion angle gas to be adjusted to compensate for the engines ability to torque the rear end up. A big powerful engine and a very big starter gear (like 10/11 or more) will need more compensation than a little engine, an automatic and 2.76s,say. Also in the mix are the rear springs; the softer they are, the more compensation will be required.
For street suspension and a stock 360 with about a 3.55, a 2250 TC, and a 2.45 low, perhaps 4 degrees is enough with SS springs. But perhaps 7* with the factory springs.
By 400 hp and a 3000TC and 3.91s, and SS springs, she might need 7* compensation.
This means that when the power is off,and she's just cruising, there WILL be vibration, that's just the way it is.
To help you get started, have a helper get in the driver's seat, lock the brakes, put it in low.You, meanwhile, go get eyes on the pinion nose. At your command have the helper slowly apply power,with the brakes locked. You watch the pinion climb. You will have to compensate for that climb,and more, cuz the brakes are gonna fail to hold at about 2000 to 2400 rpm, but full torque may not be reached until 3800rpm or more depending on the build spec.
Happy compensating.