Rim size is 12 standard Tyre is 155/70/R12
You can use 165 / 80 /R12 size tubeless Tyres
the silencer mufflers are not scrapped due to road clearance. These are rusted due to moisture. You shall visit saeed manzil silencer shops and change the units. make sure that system hangers are at correct angle(s) and rubber insulators are in place.
long ago i had a Swift 1991 (khyber) in Karachi and used to travel over super highway and national high way with friends. Tyre size was always 165/80/R12 Bridgestone Japan used to be available from legal channels. There were never under carriage scrapping issues or silencer scrapping. Exhaust Muffler rust was problematic till such time i got complete custom built for Rs. 2000 in those days.