1970 chevy stepside

[1970chevystep]

hello. i am looking for a set of rims for my truck. i am a 16 year old and my truck isnt lifted but me and my dad put heavy duty suspension on it and it rides a little higher. i have two choices right now, get some fairly new alluminum rims and then i can run the size tires i want. (budget). or by some from from the store. i want to run 31x10.50 15's. but if i buy from the store i'd have to get 16's because we already have two new sets of tires that work. i measured the tires and they turned out to be 29.5-30 in tall. if any one has reccomendations on the truck i would appretiate it. also does any one know the corrrect backspacing for a c-10 with drums all around.