He's not saying to change the
tranny, he's saying to re-use your Mustangs
tranny and bellhousing (large, dome-shaped housing that covers the clutch, flywheel, pressure plate, and throwout bearing. It's bolted directly to the engine block, can't miss it.)
A 2.3T, five speed, and decent rear gear (most 2.3s are in luck in that regard, usually having a 3.73, but not always) will give you a FAST car that gets fantastic gas mileage.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4
tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)