440 duster swap

You're in the right part of the forum- Big Block A body Tech. Start searching and reading all the posts you can, they go WAAAY back. People have been doing this for decades, so there are no surprises- it's ALL been done before, ever since Ma Mopar gave birth to the big block and A bodies. Plan each step of the swap. and have the parts AHEAD of time. Don't get caught in the trap of building your ultimate big block and then discover you have no way to mount it or run exhaust, or this and that won't fit with power steering or A/C... Get the right parts the first time and you'll only have to buy them once!
Also go to bigblockdart.com and start reading everything. Know the swap inside and out before you even start, every step of it. Research is an investment that pays dividends in time saved, money saved, and a better finished product. DON'T "go into it blind", there's no reason to. Plan the build, every nut and bolt- and ask specific questions when you're stumped. There's a good group of people here who are willing to help along the way, but not build it for you- you have to be willing to do your own legwork. Best of luck!