Hard to believe a carb can give more power. You can improve the air flow of the "beer keg" intake by cutting the runners shorter internally. A guy on ebay sold templates and instructions, plus other upgrades. That would give more high rpm HP, at the expense of low-end torque. You could also put a throttle body on the M1 intake if you think that flows more. Look for a Holley Pro-jection 2 on ebay. I have seen just the throttle body for ~$30. I think you could have the Magnum MPFI wiring drive the TBI injectors, since Holley's Commander 950 works with either. The 98 might be "alt bank fire", in which case 4 injectors are tied in parallel. Find those with a multimeter and connect to one TBI injector. And the other group to the other injector. The computer won't know it is pulsing TBI injectors instead of MPFI ones. Have the Magnum computer continue to control the spark ignition either way.