I'd totally ride it as-is, then change it to my liking. I'm not afraid of the drivetrain or wheels if they're working ok. Doing the V brake conversion isn't difficult if you want to, but pretty much all tandems this age have wide cantis with the drum being an upgrade option.
When I was shopping for my Burley I held out for a V-brake and SIS bike - especially the index shifting, because all the supposed charm of feeling the shift goes out the window when your drivetrain is five feet behind you and you have a partner waiting on you.
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Genesis 49:16-17