You won't need to swap the drivetrain.
You will, however, need to do one of the following:
With STI:
New stem (26.0 vice 25.4 clamp).
New brakes.
"Brifters".
Without STI:
New stem.
Dia-compe 287-v levers.
Bar end shifters.
P.S. How does my new red star look?
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Good night...and good luck