Indygabo:
I do not believe that Coronado ever made a 27 foot topmast sloop, although the term 'topmast' is a bit at odds with the term 'marconi'. Topmasts were usually associated with gaff and gunther
rigs.
The Coronado 27's were also later built by Aura/Hughes so you may be able to find literature on the updated version. One word of heads up, many years ago I worked on what I believe was a Coronado 27. This boat had a bolt on cast iron keel and the galvanized iron keel bolts were competely shot. If you have not checked your keelbolts, I strongly suggest that you do. (For what it is worth, I think the 41's were built the same way.)
Good luck,
Jeff