Is it possible to swap out the old ECU and put in something a little more modern? If so who makes them?

 

Holley EFI

MegaSquirt(R) FAQ Main Page

 

Pull the system from a 1996 4.9L, it's Mass Airflow and doesn't do Batch Fired injection. Batch Fire injection uses two banks of 3 injectors and wastes a lot of fuel, and AFAIK is the main reason for the air pumps for the catalytic converter to burn the extra fuel. Also, using a '96 is somewhat more legal and even has an OBD-II port.

Then you might be able to get a custom flashed PCM for added fun

If legality is of no concern or can get an exception, use the above systems or even a VEMS like I did.

 

Batch fire does not waste fuel, The reason for MPFI was to reduce emissions under 2000 RPM only by allowing the injector to pulse when the valve was close to opening or open. After 2000 RPM, the valves cycle faster than the injector can duty cycle so it may as well be batch fire again, ie cycling into a closed valve runner. Air pumps fed the cat with O2 so they would get to catalyst temperature, modern ECU's manage better so air pumps are not needed.