What can I expect?

[4th Gen C-10]

I have a 69 C-10 LWB that I am tearing into. Original plan was to take out the 307 and 3OTT and replace with a ZZ4 crate and 700R4 transmission. Thinking more about it I kind of want to keep the 307 for historical reasons. The engine has ~210,000 miles on it with one rebuild at ~160,000 miles. I am not sure exactly what was done to it.

My first question is what kind of HP and MPG can I expect out of it if I change out the cam, intake manifold, put on an efi, change out the exhaust manifold for headers, etc? So basically I am asking what would those of you that have alot of rebuild knowledge do with it?

Second issue: I do still want to swap out the 3OTT for an automatic tranny. What would you recommend to go with the rebuilt 307?

Third issue: This will be a nice daily driver with some long road trips (hopefully the Power Tour someday). What rear end gear ratio would you go with?

Thanks