Is it a straight thru design, if there are no arrows I think it just depends on how loud you want it. personally I would throw the muffler away straight pipe all the way, but I think that if you position the louvers so they go into the exhaust flow it will be quieter.

 

I love the sound of a straight piped 12v, but that is just me. If you want it load point the louvers towards the back of the truck, pointing towards the engine will quiet it some.

 

It won't matter. In a couple of months the louvers will be packed with carbon and it'll sound like a straight pipe.

 

The muffler should go in the gasser, and the stack's should go in the diesel.

 

whats a muffler?