I have a stock 73 and I want to upgrade Alternator and still remain stock looking.  I am planning on using 75 -77 280z Remanufactured Hitachi 60 amp regulator (Remy 14118) and get a 1977 solid state external regulator.  Are there any modifications, like change support brackets or wiring?

You'll have to change the connector on the 1977 voltage regulator. You will have to compare the wiring diagrams to set the pin-outs for the new connector.

The proper connector can be found at http://www.vintageconnections.com

So that is the only change?