Rockett 111 will have enough octane for a 1975 and work well. Oxygenated fuels aren't allowed like the Rockett 100. Some useful info is on their website:
http://www.rockettbrand.com/
If you run a stock gas tank, it would be best to seal it off during storage so volatiles won't evaporate, possibly causing you to fail fuel check. For example a non vented cap, and a shut off valve in the vent hose at the tank.