There is no free lunch - the cheapest way to run your 260 is to make sure
it's in good tune, with clean oil and antifreeze, and drive it regularly.
You can put a small four-barrel carb on it with a Edelbrock Performer
manifold, and the CAT or Sunbeam Specialties headers, but other than that
the cost will quickly go way up and you'll be far better off to start with a
Mustang roller-cam 5.0 engine. Right away you'll get 42 cubic inches extra,
as well as a better valvetrain for any other performance mods you will be
doing. Clean up the 260, put it on an engine stand, and save it for a future
Having said that, you can significantly improve the effective performance of
any engine by reducing the inertia of everything that it's trying to move.
For example, going to a lightweight flywheel allows more of the engine
torque to be used for acceleration. Billet aluminum and steel flywheels are
also safer than the OEM cast-iron flywheels. You can also get lightweight
clutch/pressure plate assemblies.