Tough call. Is the Fiat carbureted or injected? The 78 240 might or might not have the Lambda-Sond O2 sensor system- I think only the GT models of that year (or California models) were equipped. Both of my previous 78 GTs were equipped. This system monitors exhaust gasses to adjust the fuel ratio for lowered emissions.

Bear in mind, with injected systems, lower emissions = better effeciency = best power. If the fuel is burned cleanly, you're getting the most power out of the mix of air and fuel. Running past this ideal ratio of fuel to air to a rich fuel mixture might only see a gain of small power increases at high rpms.

I've always followed the conventional wisdom that a properly tuned car will have the lowest fuel emissions, best economy, and yes, the best power.

adjusting the fuel distributor to enrich the base fuel mixture is a science that involves at the very least access to a CO exhaust analyzer.

If you're looking for cheap power out of this motor, I'd make sure the engine is in good shape and then convert the cooling fan to an electric unit. Remove any non-working belt driven components like the A/C compressor or convert to a manual steering rack. The less stuff the motor needs to turn the better- I removed all of the above from a B21F and found the motor to be a little freer reving and more fun to drive.

Good Luck-