Single or Twin turbo setup for 360?

How heavy will you be towing? A single cheap Gt45 would meet your goals, and be very easy to plumb in that truck. I would just worry about making boost at too low of an RPM while towing.

Personally, a Cummins swap would be my choice in that thing. It will be easy to swap in, do everything you want with better fuel mileage, and cost will be close to turbocharging your 360.