what does it take to swap a big block in a duster ?

For boost and pro touring, I'd get a B wedge 400 block. It's as light and short as the 383 which will help the packaging and handling; and it's bigger bore than the 440 and has the stronget lower end of any factory block. If you are planning serious boost you may want to look into the Keith Black aluminum B wedge block. MUCH stornger, the machining is truly ready to assemble, and it's going to be a lot lighter which can only help the handling.