1967 Barracuda - Slant Six (orig) or 440 Big Block? Daily Driver, Need MPG

Decided to stick with the slant. I can order a kit for around 400 and the machine work will be ~500.
I know it wasn't the smartest decision to get a non operating car while I'm young. Hell, the reason I did was I was making a lot of money at the time. After high school, I didn't set up my university tuition but didn't go cause I sort of left/kicked out of my house (father issues) that summer. (~1800-2000 a week) and had another truck to use at home..
But when I came home my uncle ruined my truck, my mom needed help with her car payments and rent, and I started using her car for the time being. Now I'm leaving her with it and moving out of town ha. I didn't make the best decisions...