A PLRI (Parallel Logic Radio Interface) interface was designed by a friend of mine K0KN. You may refer to his site at www.qsl.net/k0kn. Then click on the PLRI section. You can also find information in Wikipedia about PLRI at http://en.wikipedia.org/wiki/Plri.
I have built two PLRI interfaces myself as well as K0KN's circuits to go along with the interface. I can say they work very well.
The Main Reference to this is the K0KN website:
http://www.qsl.net/k0kn/ , then click on PLRI Circuits
Here is picture of my Interface that is being used with my Motorolas.
Here are some pictures while in production....