4/6 drop wheel and tire question

[Jonboy]

I am planning on dropping my truck 4/6 soon. I will be using Belltech spindles, and cutting the factory spring in the front. I found a set of clean slots that are 15x8.5, with a 4.5" backspace. This brings up two questions.

1. Will they fit?

2. If so (hopefully), what size tire can I run? I would like to keep the same size all the way around. Will a 275/60 work? Using these wheels would save me a good bit of coin, just worried about fitment.