got new victor reinz MS15315W. what im questioning is on old gasket way in the back was blocked off with only a small hole in center. these new ones are open. is this going to be a problem or just wrong gaskets?

 

Doesn't matter. If you pull the manifold and look at the rear, where those coolant passages are in the gaskets and heads, you'll see that they are closed off in the manifold. This is typical of all SBC V8s.
A sort of exception is some later engines like the Vortec TBIs where the heater inlet takes off from the rear of the passenger side cyl head. There you need a gasket with a open passage.

The passages are in the rear of all SBC heads because the two cyl heads are the same casting. They were designed this way so that one casting can be used for both banks of the engine. Saved production costs. The one difference between the two heads is in some cases the accessory bolt holes are not all drilled in both ends of each head.

 

i didnt even recognize that before.ty.