As per the previously referenced issue it’s based on 1511 (7.2) as the 7.3 came out just after the new 7.2 based Rockstor iso had been prepared.
Yes that was also the finding of others, hence the push at the time for a 7.3 based installer; but the timing just wan’t right unfortunately. In the issue @tazzydemon 's explorations were referenced, re-referenced here for ease:
My kernel boot options suggestion was as an option to pursue with the existing installer kernel to avoid its kernel’s issues seen my some.
I haven’t tended to this myself as yet but hopefully all that you need should be in the rockstor-iso repository:
If you find anything a-miss there please open an issue / pull request as all assistance is welcome.
Hope that helps.