12:05 Garage- ’70 Duster build

I have no idea how many people actually read my build thread since I haven't had many replies, but I'm asking for opinions on engine choice. I hope I get some replies.

I recently came across a deal impossible to pass up on very complete 5.7 out of a cop car with ~60K miles. It's so complete, I have everything from the fan belt to the tail pipes behind the cats, transmission included. So here's the question, should I go ahead with my same plan of my well build 408, or install the 5.7? The only mods I'd do to the 5.7 would likely be a cam swap. I know the 408 will have way more power, but my intentions with this car is to get in it and drive anywhere. Good gas mileage would be a plus, but not required. It would be great to hear from someone who has mad the switch to the modern motor.