There are two methods that I know of to add an intercooler to an early 76-77 930.
Step one of either course is to buy and install a tail that will fit an intercooler. I would suggest just using one from a 3.3 liter turbo.
Then either buy an intercooler and use the intake from a 3.3, or Fred Garretson's kit which handles it all. However, I don't know if Fred's kit is still available. For details, you should talk to the folks at
www.imagineauto.com
Keith
79 930