If it's the same rifle, (which it sounds like it is) it was thoroughly covered to the owner at Marlin Firearms Collectors Assn. web site, and also at Marlinowners web site.
The gun looked to be a possible prototype of the model 1889, but with no markings on it, other than L.L. Hepburn. The owner was told that a gun of this "possible" provenance to Hepburn could not be valued without an inspection by a qualified dealer or collector.
Hope this helps.

This may not be the same rifle then. The pictures that were emailed to me showed a rollstamp on the left center of the receiver, and the letters were definitely not in an even line. They appeared to be individually stamped.
I'd like to see these pictures if possible Ken.