Alternator, Regulator & E.C.U.

The regulator pictured looks like a generic old style regulator

To tell if it's mechanical or solid state either look at the underside (mechanical has two good sized resistors)

or pull the cover and see if there's a mechanical/ electrical relay, or a solid state board.

This is a mechanical relay type:

http://vintagemoparts.com/img/p/97-396-thickbox.jpg

If you have a late model (70/ later) alternator, you can use either the later model factory regulator, or ........

if you have EITHER a 69/ earlier alternator or a later one, you can also stay with a replacement but better regulator. Standard VR 128 or Echlin VR1001

These can be expensive, but are good regulators. Frankly, if you are going to a late model alternator with better low RPM output, all you need is one extra wire to hook up the factory 70/ later regulator.

As long as it works, there's no real problem with a 5 pin ECU. Remember, though you can NOT tell by looking. Many 4 pin ECUs have 5 physical pins. You must use an ohmeter to tell if the 5th pin is hooked to anything.