440 in my 66 cuda
biggest problem you will have is the exhaust. 1st i would suggest a 383-400 instead of the 440. a 440 is probably 1-1 1/2" wider then a 383-400. this makes a huge amount of difference. have you already bought the 440?
dump the power steering and get a manual box, this gives you a whole lot more room.
the seam that joins the firewall to the trans tunnel will need to be flattened to clear the trans. i welded mine on the inside and just cut the rest off.
headers are possible but will have to be custom made and exit through the fenderwells. there may be some out there but im not 100% positive.
radiator size may be a factor also. i havent gotten that far yet.
i think you will defineitly need sub-frame connectors to keep the body from twisting.
abody joe has some pics of his car that are cool and ill post a few pics of mine with the 383 and hipo manifolds. note the steering shaft to manifold clearance.
good luck and dont be afraid to ask for advice, theres lots of smart folks here.