Cool car.

But pretty much half of all the work engineers have done on cars in the last 55 years has been “making things use less fuel (and pollute less)” so you would want to duplicate their work as much as possible.

(The rest of the work has been “making them safer in a crash” and “making them cheaper to build.”)

A modern drivetrain would probably drop right in. It would change the whole character of the way that thing drives, but a modern transmission like the 8-speed zf automatic that’s in everything (all the rwd automatic dodges, BMWs and Alfas and jags and GM stuff) would give you tall gears on the highway and still plenty of pull off the line. A modern v8 with combustion chambers and intake paths and exhaust paths that have all been designed using mathematical flow modeling, would get more air more easily from the air filter to the valves and from the valves to the exhaust tips. Modern fuel injection would get the right amount of fuel to the combustion chamber mixed way better with the air and giving way better combustion than the wild-ass guess that is a carburetor and an intake manifold and 1970s cylinder heads and 1970s pistons and 1970s camshafts and an exhaust manifold, with a spinning distributor that uses A WEIGHT AND A SPRING to control its spark timing.

They are getting 17 city and 24 mpg highway out of a Ford v8 and automatic these days, in an F150 that is basically the size and weight of two Rancheros stacked on top of one another.

Taller gearing would get you part way there, which probably means “transmission with more gears” although a tall diff might help too, but there’s a lot of computational flow dynamics in a modern combustion chamber that helps them get 400 hp out of the new one while also polluting less and burning half the fuel.

The most likely answer is “enjoy it as is, buy a second more-modern appliance car to get you around when you’re not trying to have a fun ‘classic car’ experience.”