They are a torque prevailing style of nut for a low torque application, why the brass spacer I'm not certain, but it definitely is to allow the manifold to grow w/o binding and developing stresses that result in cracks etc..
If you look at and analyze the hardware the very thorough Chrysler engineers (AKA anal retentive) originally specified, it's obvious the central section of the long manifolds, cylinders 3 &4, are clamped to the head as one would expect. But with the triangular and brass washers retaining 1, 2, 5 & 6, they allowed the manifolds to expand and contract through normal heat cycles to prevent cracking of the cast iron.
The brass washers have a lower Friction Coefficient to allow easy movement AND they will not rust to the surrounding ferrous materials, which would lock the manifolds in place and lead to failure.
So my 55 year old 225 still functions like it did when new.
Oh, and follow the torque specs and use Remflex #6008 gaskets.
