what do I set the axle degres at

I am puting a 9" in a 48 cadilac and I was wondering what degres to set it at. I am welding new spring perches on I think it is three degres but I dont know if it is up or down. thanks for any help

the motor is at 3 degrees down so the rear end should be at 3 dgrees up right. but I read in super rod that the rear end should be at 4-5 degrees down and not run in parallel with the transmition. they said this will keep the u-joints from oscillating. I was going to go with 3 degrees until I read that. are they right or wrong. thanks for any advise