From what I recall the '70-'71 was a big change for the Roadrunner. The 70 (and earlier) were square, ala dukes of hazard charger, and the '71+ were rounded like the challenger. They also cam with anything from a 383 to a 426 hemi or 440-6pak. I don't know what the smallest motor you could get in 71 was, 340 maybe.
Looks like you mustang is a little bit of a sleeper with the 351 in there. He was probably been beathing 289 mustangs for years. Keep an eye out for him without the old lady, I'm sure he'll run you again.
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1997 Mustang GT "The Freak" - 13.80 @ 101.70, 2.07 60'
1995 Honda VFR750 - not much @ really fast (actual data pending.)
1964.5 Mustang 289
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