Originally Posted by
JunkYardBike
It'll be a pain in the neck!
If you swap shifters, you'll need a cassette to match in back (either the same number of cogs on the Trek 1000, or a cassette with the same spacing between cogs). Also, you'll likely need the 'light action' derailleurs on the Trek, which have less stiff springs and a floating upper jockey wheel, which all help with the indexing.
You could swap everything over, including the wheels. You might need a spacer for the front derailleur clamp, and stops on the downtube for the shifter housing, but otherwise, I think you could do it. Oh, and if the chainstays on your Centurion are longer, you may need to lengthen your chain.
On my 86 Trek 400T (pg 2) I only swapped wheels (with cassette) & shifters to 9 speed. I left and readjusted (H and L, the index is on the downtube cablestops) the original derailleurs & brakes. I even left the original crankset. I also put on a 9sp chain (but it was used).