Arches vary in every aspect. What suits one decor and client's taste won't suit another.
I've never done two the same although they all include a matching (wooden) keystone, cube and oblong ashlar.
An arch can be made in any way you want - including matching to an existing set of stones.
The one on the left was made for Coventry Lodge of MMM and on the right, Millenium Lodge of MMM.
click here to resume