You seem to be confusing CIS and EFI. If you stick with your CIS, you may have to adjust the CO mixture, but that should be it. Was the 3A on CIS or some other system, you might have to change injector seats for the CIS injectors. As for spark, that will be up to what you and what will work, depends upon what you have and need. And as for the O2 sensor, if you don't have one now, no need for one and no way to add it to CIS basic anyway.