Lesser of two evils - screamers

In answering I'm assuming the Accelerator is for a 340 / 360. In either case you are going to have a miss match at the intake runner and head which will mess up the flow significantly. 340/360 heads and matching intakes have much larger runners than 318 heads/intakes. When the airflow in the intake runner hits the restriction of the smaller port of the 318 head you will induce quite a bit of turbulance. Envision a fire hose hooked up to a garden hose. Getting an Airgap, unless it's sized for a 318, will do nothing to improve the situation. If you want to stick with the 318 heads then open up the intake ports to 340/360 dimensions using an intake gasket as a guide. Or sell both your intakes and use those funds to buy a 318 intake suitable for your combination. Don't think there is a spits bit of difference if your going to run either of the two you have on hand