How long should I break in a newly rebuilt rear end with a new ring and pinion?

The shop that is doing it said 500 miles of no more than 55 mph speeds and only drive times of around 20 minutes a piece. Does that sound right?

After the break in, should I change the fluid? If so, I hear that synthetic is the way to go, especially if you want to quiet down noisy gears (the shop used Richmond gears because GM has a holdback for the stock gears) and I'm sure these will be louder than stock. However, since they are harder, I hear they are more durable, right?
Also, is a thicker gear oil better?

Let me know what you all think, please! Thanks!

 

http://www.ring-pinion.com/gear/g0698.shtml

 

Thanks Shoebox....again!

 

LOL...I'd say my GM 4.10's got about a 50 ft. breakin.