There might be as much as a 10 percent fuel economy improvement if you were to "equallize" the eight cylinder intake runners so that they got a more nearly equal air to fuel ratio at highway cruise rpm and throttle opening.

The cheapest way to do this would be to buy or borrow an electrical multimeter with a type J or K thermocouple probe, and then measure the cylinder head metal temperature beside each sparkplug. The highest reading cylinders will be the ones closest to an AFR of 16 or so.

It would be better to drill holes in the exhaust manifold to measure EGT but this is obviously more work and expense.

Even better still would be bleed some exhaust gas from each cylinder across a wide range oxygen sensor and measure AFR. Individual header tubes make this more straight forward but it can be done with exhaust manifold holes "collecting" gas to sample.

Port the runner of any cylinder's intake manifold that is too rich and therefore is lower in temperature.

Boosting static compression ratio from 8 to 11
would give roughly 8% fuel economy gains
at part throttle cruise,
but detonation at full throttle unless you used water injection or cooled EGR.

Back around 2004 then Chrysler chief Tom LaSorda wrote that switching to optimum economy camshafts instead of 4500 rpm max power grinds would improve fuel economy about 6%