Best way to connect a Single Pass Heatercore?

Hey all, just installed Watercooling with some parts I had lying around and now I would like to change things up a bit.

Currently, I am running a Ford 2x Pass HC in the top of my case with 1 120mm fan pulling air from top of case. Waterblocks are DD Maze3 and Z-Chipset, pump is VA 1300 all with 3/8 Clearflex.

Just picked up a 2-149 single pass HC which will mount in front part of case with dual shrouds and 2x SVC 120mm fans with 7v mod.

My question is this: What barb would be input and what barb would be output considering one is on top of HC and the other is on the bottom.

I don't think there's any difference.
Suma.

Well, if I fill from the bottom I am assured it will fill the entire HC, but maybe at the cost of more work for the pump.

If I fill from the top, gravity will help but I am not assured the entire HC will fill.

The entire HC will be filled anyway, you can't have air in your water cycle.

Oh yeah, LOL!

Yup like Suma said it doesnt matter just choose whichever gives you a shorter tube length