I have a 400 engine in my 72 Challenger and was wondering if the headers I have now will fit a 440 engine if I upgrade to that or do I have to buy new headers? What about my 4 barrel carb, will I have to buy another intake manifold for the 440 or just put the one on the 400 onto the 440? please help and thank you

 

headers and carb. will be ok, but your 400 is a "B" block (I think 360?- late 383 and 400) so you'll need an intake for an "RB" (early 383-413-426 wedge-and 440)