68 dart GTS 18 rims question

hi all, luke here Australia/oz, I have a 68 dart gts(standard 8 3/4 diff with pirate jack front and rear disc brake conversion) and stock leafs and tubs etc... after what 18” rims I can get with size and back spacing and Tyre size as well...just to help with ordering /looking on summit racing ...we are heading to Hawaii in September and can get parts sent there (and bring back on a cruise home) ....

Thanks for the help...
Luke