Considering the cost of doing a fully supported coast 2 cost tour, a new bike is a marginal additional cost. The next long weekend, ride three days in a row, approximately 100 miles daily in a moderately to very hilly area with a few steep ramps. If you are comfortable and the bike meets your needs, go for it. Romance of reliving the 70's aside, I would buy a new comfortable adventure bike for the trip with a wide range 2x11 system such as GRX and tubeless tires. Things have progressed incredibly since the 70s, and you should enjoy the benefits of this progress.