Best way to bypass heater core...

Parts stores carry a molded hose in stock that is a U shapped and has different size inlet and outlets. Off the top of my head I cant remember the part number but I would try and find an advance auto parts or Autozone that will let you go to there backroom and look at their hoses, youll be able to point it out by looking at it. They should have there molded hose organized, big radiator hoses together, and small bypass hoses together. If you really cant find it I could get the part number from my work in a couple days when I go in.

You can also just ask them to go back there and grab all the molded u shaped heater hoses they have in the back (not radiator hoses) and they should only come back with like 1 or 2, measure them to make sure on side is 3/4 and the other is 5/8 and you should be good to go. If they give you a hard to time ask if there is someone else that can help you, I wouldnt have any problem doing this for someone while I know some people at my work would be like "If I cant look it up by car than I cant find it."