Correct. It's a YZ400 engine/frame/swingarm with XS250/400
wheels/brakes and an RD250/400 fuel tank.
Looks like he's chopped the exhaust to sling the expansion box under
the engine and fabricated a twin outlet.
I like it, even more so because it's dirty.
--
Lozzo
Versys 650 Inter-Continental Hyperbolistic Missile , Cagiva Elefant
900, CBR600F-W racebike in the making, TS250C, RD400F (somewhere)