I have always ran a 2" spacer on Air Gap manifolds on my small blocks.

I've used 2" open and 2" Super Sucker style spacers with success. I usually just radius the divider

I did see on a Facebook group post where someone used a modified 4 hole spacer in a different manner. The spacer was turned in to a three hole spacer, one side was opened up to match the intake, where as the deeper side of the intake\, the spacer was left as a four hole. They also dimpled the floor with a ballnose end mill. If I can find the pictures, I will post them.

Cheers