Air gap versus MP M1?

Great input! Ok, long story but i'm just trying to get this thing on the road so my kid can take it to prom next spring. Right now it is a stock 340 with X heads and headman street headers. 3.91 rear. The long term plan is to go big with aluminum heads, stroker kit, mild stall, the whole shabang. I want some more punch for the long run.