Sorry if this question's title isn't clear. I feel a bit out of my depth on this one. Got to this point via a somewhat convoluted route...
Trying to migrate old AGS map services to Portal. These maps appear to be derived from CAD drawings and features were reprojected to essentially line up with the page or window of the GIS application. So what you see in the map does not match the real world alignment of features. The originals are in MXD form and there is no rotation in data frame. The original map services apparently accepted this transformation and showed the features in the desired "format".
When I import MXD's into ArcGIS Pro (2.5), everything looks good. When I publish to Portal, everything still looks good. Map services show the feature transformed as desired. But when I create a web map from these web layers in Portal, everything apparently gets forced into the basemap's projection and all the sudden everything appears rotated back to its real world alignment.
Is there anyway to override this - to make the webmap use the map service's projection? I don't see that there is a way to remove the bsemap. The ESRI definition of webmap sorta implies use of one. There is virtually no way to do anything else through Portal interface. But I see that through Python API I can get a reference to the webmap. However, it shows that the property
Is there any way to use a different projection from basemap?
Ultimately, I'd like to build an app in Web Appbuilder with these layers, so maybe I could configure this over the mapOptions in congif.json and the spatialReference there? I haven't looked at that yet.