5.3/6.0 swap questions

[1984 t type]

Thinking about doing a swap and had a few questions.

First how many miles are ok for a good swap candidate? I don't want to rebuild the motor just drop it in and go.

Second does anyone know the difference in mpg's between the 6.0 and 5.3 motors ? I don't plan on doing any regular towing so I'm thinking 5.3 but if I see a good deal on a 6.0 I will go that route as long as I'm not giving up too many mpg's since that's the purpose of the swap.

And third, I'm sure I asked this question on here before but will I be giving up any mpg's going with a 700r4 over a 4l60e. I only ask because I have a freshly rebuilt 700

Thanks for your help guys
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