Either can go fast, since both commonly use similar small blocks. Early models have less emmisions restrictions, but late models have better manual transmissions. A 5speed w/low first gear makes a big difference. I prefer early 64-69 fastbacks styling. I think the best drivetrain combo would be a 351W with a 5 or 6 speed tranny. I like the 351 because it is very similar to the 5.0 so it has benifitted from the new heads,cam etc. technology. Any engine and tranny combo will go in both a 60's, or 79-93 mustang without much modification. I think that big-blocks are not a good choice because you can build a 351W to run with any street big block for a fraction of the cost. If you want big-block displacement, you can stroke the 351W to 427ci or higher (and it weighs a lot less). So both have about the same performance potential, the only thing to decide is which styling you prefer.
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67 Fastback - Arctic White Pearl paint
351W 415 hp, Trick Flow Alum. Heads, C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.
