want to bipass heater core as leaking into passenger compartment

I am afraid I don't know but would suggest calling a Napa or good auto parts store, tell them you are stranded and need help, they have a listing for heater hoses if they have it i stock they can pull it from the shelf and tell you what inner diameter the hose is. Call them first thing in the morning hopefully they won't be so busy that they can't help you.

either 5/8 or 3/4.i believe it is 5/8. you could join the fittings from the intake to the water pump without installing a copper bypass. follow the hoses back to the motor and join the fittings together. Roy