tire size for dropped burb

[xman]

I know this has been covered sometime ago but I could not find it for some reason. I am planning a small drop on my 72 burb 2 front and 3 rear (both are spring and shock) and I am just wondering what everyone else is running for tire size I am going to be running 15x8 truck ralley wheels
Here is a pic of what I am working with

If anyone can point me to the correct thread that wouuld helpfull also

Thanks in advance
Dave