Here's an example of a nice S3 custom. RZ350 front and rear ends... nice!
I've tracked down an S3 (400 cc triple) in a local junkyard for a song and I'm seriously considering risking divorce and picking it up. It's covered in rust but there is enough of it left to build a serious custom. There are even pistons and chambers available for them now. I keep telling myself that I need to this the herd but then I keep finding good deals. I've already passed on an $800 RD400 Daytona and another S2.... Here's a video to the boys in Europe who are selling those S3 stainless steel pipes. About $1000 after currency exchange and shipping.