The least expensive, but do require custom hardened pushrods, and will not work with stock rockers or valve covers (unless you feel like grinding away the inside of your stock ones). You should be upgrading this stuff if you want to race the car anyway.
I run TFS heads with a mild port job.
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1988 Mustang GT
11.8 @ 123 (7/14/01)
1992 BadAzz Wrangler
1993 Explorer
See my car at:
www.mustangworks.com/cgi-bin/moi-display.cgi?179