I love the Sunn! Those shiny skinny tubes really do it for me.
I saw a similar frame here in Brussels a few weeks ago, chained to a fence right outside a bar I was drinking in. I didn't take any pics as I didn't want my GF to think I was a total weirdo (she already has suspicions ...). It was fully rigid with a curved silver fork the same finish as the frame. There were a load on stickers saying 'Sunn' and 'Mountain Force' on the frame; on the one hand they all looked legitimate, while on the other they could have just been stuck on. Do you know anything about such a Sunn bike?
Next time I see it I'll definitely take a pic ... and leave my phone no on the frame in case it's for sale