I would think that your local auto parts could order them for you. Summit carries them. Also a company called Ersco in Texas carries them along with all kinds of valve train parts. I don't have their number but you can call ASP (281 261 8845) for their number.
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88 347, Twisted wedge heads,Comp Cams 224/230 cam, 1/4=10.718 @ 123.02 mph,dyno=
=http://www.fbody.com/members/LarryS/mustdyno.jpg