Big Block or Small Block in my 70 Duster

I'm sure this has been pondered by many, but I have to ask: how much of a pain in the donkey is it to put a big block 4 speed combo in a 1970 Duster? Can I run power brakes and steering or isn't there enough room? I've looked at pics and it seems like a tight fight.

I've got a fresh 440 in the garage - this is why I ask. Otherwise, I have to rebuild the 340 that came with the car or rebuild one of my 360's. I've got the full four speed setup for the small block, but will need to find a BB bellhousing and such for the 440.

What are your thoughts?

Thanks for the help!

The Newbie!!!