My cousin is a big mopar guy, who wants to give me a 440 engine for free that came from a 1975 chrysler new yorker years ago. It was my grandfather's car, but my cousin saved the engine. He said he'll give me the 440 engine for free with only 45 to 50 thousand miles on it. My truck currently has a 360 in it, and I was wondering if I should take the 440, have it rebuilt, and throw it in. How much work will it be, and does a 75 440 run on unleaded gas? If it doesn't, can it be rebuilt to not run on leaded gas? Thank you.

It'll be some work and $$$, you'll have to change the motor mounts, oil pan, exhaust manifolds, maybe radiator.
The biggest thing probably would be your transmission, you'll have to find a BB auto trans or a bellhousing, flywheel if a 4speed truck
And you'll get about 8-10 mpg, which is what I usually get, SO don't get to drive it too much any more...
Sometimes it's better to have a bigblock donor parts truck to scavenge parts out of. Small block parts are plentiful and big block stuff is getting scarce and pricey.

'72 up yrs engines I think have hardened valve seats for your unleaded gas.

Good luck!

-Jim