From ” The Stirling Story “, by Bowyer
Stirling LK618 was flown to USSR Jan 4, 1945. It suffered a flying accident on the 14th when the ASI went unserviceable during takeoff and the undercarriage collapsed during remedial action. LK615 was sent to replace it on Feb 28. It flew from Melton Mowbray and was delivered via Shaibah and Teheran, arriving in mid March.
A photo on page 243 has this to say,
Mk.III LK615 was shown to the Soviet Acceptance. Commissioned on 1 March, 1945, it was rejected as incomplete. It received attention at RAF Habbaniya before handover at Tehran in summer 1945. Flight tested at L11 NKAP ( Flight Test Institute of the People’s Commissariat of the Aviation Industry ) by G M Shiyanov, he considered it far more difficult to handle than the B17/24 tested at L11 Zhukovsky ( Kratovo ). The Soviet Air Force never tested it.
more here
http://wp.scn.ru/en/ww2/b/443/1/0
http://www.stirlingproject.co.uk/Newsy10b.html