Dist Question (Sitting on hold)

I swapping the dist in my car. I've got a carbed older model 302 and somewhere along its way, it ended up with an EFI dist. My question: the other dist that I've got with the vac advance is about 1/2" (the shaft below the gear) shorter than the EFI dist. What probs does this propose if any? I've got a duraspark box that I'm going to install.

Thanks