Well, I don't know about 27" wheel sizes being obsolete. You can still readily get 27" tires in any bike shop or departments store. Oh, you can't get specialty tires, or kevlar tires, or colored tires in 27", but you can get enough road skin to put on thousands of miles.
As an alternative, think about using old tires. It is one of the best things a bike rider can do for the environment besides chosing to bike rather than drive. You can get used tires and wheels for just about nothing. With a few rare exceptions, most of the '70's lightweights hubs were made by Shimano and were similar in design. Rims were similar enough not to worry about, especially if you are a utalitarian or pleasure biker.
This means that you can buy a second or third bike as a spare parts bike.