What Steve said, pretty much.You can go to any parts store, or order the muffler from any catalog place. Just gotta know what size inlet you need. I believe it's 2 1/4", but double-check that. I got the DynoMax for my '77 from Trak Auto actually.
As for a ram-air set up...you'll probably have to fab up something. Here's also a link to "Project 77"...a '77 Ghia that had a custom ram-air system installed, using an air cleaner assembly from an old LTD:
http://www.mustangii.org/gallery/project77/
If need be, I could get you in touch with the car's owner when the transformation was made. He may be able to tell you more about what he did.
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Frank S.----MCA Member 40390
'03 Mustang GT coupe
'99 Mustang coupe
'77 Ghia--"II Good"