engine swap small block or big block?

well i gave up the dream of putting a v8 into my dart til i saw those shumacker kits and now its got me dreaming again lol my dart currently has the slant six in it and i will be buying a beater so gas mileage will having nothing to do with the motor i put in.it will be my first swap but i got a couple buddies that know what there doing that have said they would help and im pretty mechanically inclined just havent had the chance to really do anything like this before(not really any car guys in the family)so is what im wondering is what are the pros and cons for small block and big block ive been looking on craigslist and its about the same for a old 70s 318 or 360 as it is for a old 440 but what about parts generally speaking is it more for big block parts? i dont want to do anything to extreme so internals wouldnt matter i would be leaving whatever i get with stock internals but i mean heads and intake and headers and such is there a big price difference?also will the big block screw up how the car handles with all that extra weight? also does an old 440 get decent enough mileage to take on long cruises?sry if these seem like newbie questions but im still learning lol its always been my dream to have a 440 in my dart just cause its the granny model (74) and no one would expect it lol would be a cool sleeper