Slant Six - exhaust manifold hardware?

Referring to the attached photo, the pair on the right is directly off of a slant six in a 1983 Dodge truck. The washer has a straight center while the nut has an extra tapered edge to fit into the washer.
The one on the left is aftermarket, the nut is straight (no taper) and the washer has a bevel in the center for the nut.
I am just wondering if the aftermarket one will work as well as the OE setup because a new factory style nut is impossible to locate.
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