which motor for daily driver

[DMCK]

Hi, I am fairly new here. I have a 71 GMC 2500 4x4. Originally bought it for my son when he got his learners at 14. Over the next 2 years we worked on it to get it ready for when he got his licence at 16.
He drove it for about a year, and now I bought him something more reliable.

So now its mine

this has probably been beaten to death, but i am going to buy a crate engine
and not sure if I should get the 260 or 290hp 350.

I want the warranty, it will be a daily driver, regular fuel, best mileage of the two??
turbo 400 trans is getting rebuilt now and new torque converter will be a little bit higher stall speed from stock, if that matters much.

any feedback appreciated
thanks.....Dave