There was a US50,55,60,63H,70 and 75 They were all 52" tall with the rounded case design,grand style fallboard and the large music rack. They were actually the predecessor mdls.to the US6X and the US8X which were the predecesors of the
K-80 which was the precessor to the present K-8
I've always felt they were the sleeper mdls. in direct competition to the Yamaha U3 which one sees more often.The US55,63H,70 and the 75, I believe were not sold and marketed through Kawai USA but are present grey market mdls. The US70 and 75 were the high end mdls as for the gray market mdls.They were of the traditional squared off cabinet similar to the Yamaha WX7 /U5 case design. They had agraffes and believe it not had two extra strings in the bass,low G and G# which had no hammers or dampers and reasonated sympatheicly.If of low milage they are great pianos. None of the US mdls. had a sostenuto function except the later US8X,K80 and the present K8.
Now you are an expert and could teach the dealer a thing or two about this US series. Good luck!