Let's say that I am willing to put any type of engine and drive train into an early 60s car to increase MPG?

Old Chevys and Plymouths were obviously heavy, but what can be done 'today' to increase fuel efficiency when you are replacing the engine in an old chassis? Can a current GM engine go in or is it not worth the expense?Let's say that I am willing to put any type of engine and drive train into an early 60s car to increase MPG?
Putting a modern drive train into classic iron is a GREAT way to make them more efficient, reliable and keep them on the road. There is a lot of room in those old engine bays so you can put whatever you want in there. You should realize also that todays cars are heavy too, with all the safety/comfort options. For example, a late 60's early 70's Nova weighs less than 3000 pounds, a new Mustang or Camaro is 3600 or more. There are plenty of conversion kits out there to make the electronics work. It isn't cheap, but if you like the car then it is very worthwhile, and makes your old car more fun and drivable. The overdrive transmission itself changes the game, you can have hard acceleration AND comfortable freeway cruising RPM. You could be saving the world too, think of the enviormental impact of every new bic lighter car that is built! And then crushed in a couple of years! Save the classics, and drive them!Let's say that I am willing to put any type of engine and drive train into an early 60s car to increase MPG?
Sure, you can put new GM injected motors in old carsLet's say that I am willing to put any type of engine and drive train into an early 60s car to increase MPG?
Use the money you were going to use to replace the engine, etc and spend it on gas.