My understanding is that the valve is mainly to prevent the flame from a header backfire from possibly igniting the oil vapors in the valve covers and crankcase, not so much reversion.
The valve you have shown has -8 fittings, while the evac kit appears to have at least-10, although I can't see it called out. It's best to not restrict the line by reducing, so if the valve comes in a size to match the kit, that would be best. Of course the line and fittings down to the valve covers should match that size also.
It would be really clean if the valves came with 1/2 female pipe x -10, then you could eliminate that big AN fitting in the kit.
