Let's pipe dream about sequential port injection and one coil per cylinder ignition.
If we are talking naturally aspirated the I would use the 250 for the extra low rpm torque.
The Aluminum head will give you the extra pep plus being aluminum you can run a higher compression ratio than the iron head which will help increase fuel mileage along with additional torque.
The head has injector bosses that will direct the injectors closer to the intake valve.
You will need to machine the bosses for the injectors and machine a fuel rail for the top end of the injectors.
The fuel rail will need supports to hold it in place
One end of the fuel rail receives fuel from the fuel pump and the other end runs to the fuel regulator that has a return line back to the fuel tank.
Fuel pressure minimum is about 45 psi.
Use an in-tank fuel pump.
A round throttle body can be attached to the 4 barrel carb intake using an Edelbrock Intake Elbow.
The throttle body has the TPS sensor and the IAC to control the idle rpm.
Most EFI ECUs have an internal MAP so you just need an 1/8" hose from the intake manifold to the nipple on the ECU box.
The intake manifold will need another threaded hole for the Manifold Air Temp (MAT) sensor.
Need a coolant temp sensor in the side of the block.
Need an O2 sensor in the header collector
Optional:
Oil pressure sensor
Fuel pressure sensor
Knock sensor
If we are looking for max MPG, the cam profile should have a wide lobe separation angle (LSA) to minimize valve overlap.
Using a long tube, small diameter header will reduce pumping losses during the last half of the exhaust stroke and the wide LSA will prevent raw fuel from being scavenged out the exhaust by reducing the overlap period between the intake and exhaust valve opening.
For best ignition timing resolution, attach a 60-2 tooth timing wheel to the harmonic balancer hub.
Most ECUs will support the 60-2 plus other wheels with less tooth count.
The ECU will also need a cam sync signal to mark cylinder #1 for sequential operation.
That can be done by modifying a distributor.
You can also modify a cam sensor from the 3.8 V6.
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Add an electric radiator fan and you have a good start.