8bender:

An '84 or '85 380 in good condition, low miles, etc., could be the best buy. The early engine timing chain matter is in the past for those years, and should you wish, a 420 engine is a bolt in (both are M116) if the original injection system is retained. The 420 injection could be used with a change of some of the wire harness.

From the standpoint of the basic structure of the car, suspension, driveline, etc., 380s and 560s are essentially the same. Detail differences from year to year. Larger front brakes on 560s; can be retrofitted to 380s.

As with real estate: condition, condition, condition.