Have you searched the FacetDiagrams site in ovals alot there to choose from. You can try the 1210 Oval by Robert Strickland is somewhat similar. Is 1.33 very close should not present a problem. You can tangent ratio the original to fit your RI range if needed. This is the design 02.175c OMNI Oval 1.33 I can adjust it for your 1.72-1.80, if your wanting it to be 1.6 you should use it as it is designed 1.54.