???
I'm puzzled because the Skopar is a tessar type. Typical cross-section here:
http://www.dioptrique.info/OBJECTIFS12/00551/00551.HTM
Lenses badged Heliar can be like the original Heliar, cross-section here:
http://www.dioptrique.info/OBJECTIFS8/00370/00370.HTM, or the original Dynar, cross-section here:
http://www.dioptrique.info/OBJECTIFS8/00371/00371.HTM.
The Dynar's rear group has the same form as the typical Tessar rear group, the Heliar's rear group has the same form as a reversed typical rear group.
So, how can you tell whether your problem lens' rear group is a Skopar type or a Heliar, so badged, type?
Also, why do you think that a randomly selected rear group that fits the problem lens' shutter will make it right?
Have you eliminated the possibility that the lens was disassembled and reassembled with the central singlet reversed?