Chengdu seems to have devised its wooden SB derivative in reaction to the longevity of that aircraft in Chinese service (compared with the DB-3). The SB M-103 (or SB-III as the Chinese called it) served on in operational units in 1943 when the few remaining DBs had already been passed on to training units.
The site listed by lucamax lists the engines and wings as "native", suggesting components 'recycled' from Soviet-built SBs. Certainly the engine cowling look like units from an SB M-103. But the claim of metal wings was reputiated by Anatolii Demin in Soviet Fighters in the Sky of China VI (1937-1940) in Aviatsiia i Kosmonavtika 2.2001 (translated on j.aircraft.com by George M. Mellinger).
http://www.j-aircraft.com/research/George_Mellinger/soviet_fighters_in_thesky_of_vi.htm
"At the aircraft factory in Chengdu they undertook an attempt to copy the SB. Despite the contrary opinion that only the fuselage was original and everything else was taken from a Soviet supplied pattern machine, in fact the wings of the new aircraft were also wooden, of Chinese manufacture. ... Flight testing of the Chinese "SB" began in 1944, but after several successful flights, the aircraft was entrusted to a different Chinese pilot who "pramged" it during a landing, and it was not restored."
The following is from http://surfcity.kund.dalnet.se/sino-japanese-1944.htm
"During 1944 flight testing of the Chinese-built SB bomber began. After several successful flights the aircraft was tested to by different pilot, who crashed with it during a landing, and it was not repaired.
The aircraft factory in Chengdu had undertaken this attempt to copy the Soviet SB bomber in wood. It seems that they might have used documentation from the Soviet wooden SB project, which had been assigned to A. S. Moskolev in the end of the 1930s."
