Looking for input on wheel and tire size
 

I have a 70 c10 and I am nearing the end of the project. I am going to buy a new set of wheels and tires. It has been kept stock for the most part. That being said it has the 6 lug bolt pattern and drum brakes. Was looking for input on what back spacing to use and the proper size tire to use. How wide of a tire can i get away with without running into issues. Any input here would be appreciated. Thanks in advance