You'll need all 3 gears, the w/r input (4th gear) and a wide ratio cluster. The synchros and all the little bits are the same.
Probably not a cheap undertaking but quite straight forward. I just did the same thing but I built a RUG-AE1 into a really nice, big-in/big-out wide ratio. I had a complete
small block w/r tranny that was in beautiful shape so it was relatively cheap for me to do...
53 F100, Volare clip, 4 wheel disc 390-wide ratio toploader
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Political economist Frederic Bastiat, The Law