The break in period is one of the most crucial periods in an engines life, and it can play a large part in determining the life of your engine. I got the following information from a book called, "Drive it forever." Great book, lots of good advice. It is writen by Bob Sikorsky. (ISBN 0-9657577-0-6).
The break in should be done in the most favourable conditions possible. This means that in the first 500 miles cold starts and excessive idling should be minimized. The car should be run under load almost immediately after starting. Drive in a medium gear around 1,500-2,000rpm until the engine has reached it normal operating temperature. The engine, once hot, should be run moderately, not exceeding 2,500 rpm or 40mph (in top gear). Do not let the engine labour, and don't let the engine speed fall too low. Driving situations that call for more than half throttle should be met by shifting into a lower gear.
-Change your oil after the first 1000 miles
-The first 500-1000 miles of break in driving are best covered in 3-4 longer trips than in many short trips
-Don't run the air conditioner for the first 2-300 miles
-Occasional full throttle acceleration is beneficial when the car is already in motion. (you're driving at 40, push the pedal to the floor and keep it there until you are at the limit, then let off)
-Try not to drive at constant speed for more than 5 miutes at a time, and occassionally let your foot off the gas alltogether and let the car slow down. (this creates more engine vacuum and gets more oil into the top half of the engine.
-Never accelerate fully from a dead stop.
Your new bearings will have much closer tolerances than the old one, restricting oil flow more. Also, as your new parts break in you will get more metal in your oil than at any other time. Personally I would take it out for a 500 mile trip, varrying the speed, accelerating occasionally, and then change the oil. 3 or 4 more trips to get it up to 1500 miles and then another oil change. After that change the oil at regualar intervals, but keep the driving moderate until you reach 5000 miles.
Just my 2 cents. I really believe that if you give your engine this royal treatment for the first 5000 miles and the first 1500 especially that it will pay dividends far into the future.
1995 E420 - retired
1986 420SEL - retired