Check out Home Depot, Lowes or Ace hardware for a 5/8" to 1/2" hose splice.
Or buy some copper tubing and sweat solder it together to make your own splice. I did the copper tubing thing and made a U shaped tube with 90 degree elbows and some short lengths of straight tubing.
Or you could completely remove the hard black heater tube assembly together with the heater hoses and do this:
It's an ECT sensor elbow and it allows you to reinsert the ECT sensor in its stock location while still having a hose going from the intake manifold to the water pump. Removing that heater tube assembly also makes it much easier to remove the passenger side valve cover.
Thanks everyone we bought some brass fittings and made a jumper. We have to fix it by oct. I guess or no heat or defrosters.Sounds like a real bear to change that core.