420 hp from a mild 302? I think you might be in for a suprise at a dyno.
I run 275/60/15 drag radials and I can still blaze them pretty easily if I try, so unless you have a lot of drag suspension parts smaller 225 drag radials will not deliver what you want. A 26x9x15 slick would get ya!
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1988 Mustang GT
12.0 @ 122
1992 BadAzz Wrangler
1993 Explorer