hey Rich, i too own a DR28C Japanese made that was given to me as a gift in '82. it is a beautiful florentine single cutaway that as you say was not made in very large quantities. the later Sigma cutaways have a more rounded style and i have seen many of this type whereas, the one i have comes to a nice pointed tip on the cutaway. this guitar was bought brand new with an excellent hard- shell case and was just under 275.00. originally, it was very brassy sounding with a lot of treble but as it has aged over almost 30 years it has mellowed in tone but not in volume. i love using this guitar in open tuning as it rings out with great tone and volume. I have never seen one up for sale anywhere so cannot say what it it actually worth but if i was pressed to sell mine i would take no less than 400.00 for it.