I have a 1976 RD400C. It's the first model of the aircooled RD400 that was imported into the USA.
The bikes themselves are not really worth a large amount. I bought mine, needing some work, for 700 dollars.
The 350 Elsies don't have the kind of cult following that the aircooled, earlier RD350s, and RD400s do, but there are still people that want them, if it were a slightly later model RZ350, it would be worth considerably more.
Still, it is fairly high mileage for a two stroke, and will almost certainly need a new top end in a few thousand more miles.
All in all, I'd post it on craigslist for ~1800 USD, and ebay as well with the reserve near to that. If people get in bidding wars, you could possibly get more than that. But I think that thats the high end of what you could hope to expect.
The 350LC was what the aircooled RD350 had become, after production had ceased in 1975. They started remaking the 350s as the "elsies" the RD350LC in 1980-82. Production then ceased again until 1984, when the designation was changed to RZ350LC, or in some markets the RD350LCII. The RZ badge denoted Yamahas new YPVS, their version of a power valve system, and the new RZs had next to nothing in common with the old RD350LCs or any of the other RDs for that matter.