Buy 'em both. Refurbish 'em both. Then trade one for the Red Eye you want.
I have two Red Eye 66s in treadles. One in decent to good finish and decals, one very well used and worn. Both sew beautifully. I'll leave them as they are. No need for new decals.
As for the putting the decals on the plain machine, the Red Eyes were only made during a certain time period. If the plain machine wasn't made in that time period a knowledgeable person will catch it right off. I'm not a collector, just a hoarder. But I like to keep the machines in their original configuration as much as possible.
But that's just me.
Joe