From what I understand, Romania had converted the rail network to standard gauge prior to 1940.
In the early 1920s, as Moldova had united with Romania, the tracks were converted to standard gauge. In the interwar years the Basarabeasca-Cantemir and Revaca-Căinari lines appeared.
Soviet Union did not convert it back to broad gauge until after World War II.1918: There was only 657 miles (1,057 km) of railway; the main lines converged on Russia and were broad gauge. Rolling stock and right of way were in bad shape. There were about 400 locomotives, with only about one hundred fit for use. There were 290 passenger coaches and thirty three more out for repair. Finally, out of 4530 freight cars and 187 tank cars, only 1389 and 103 were usable. The Romanians reduced the gauge to a standard 56.5 inches (1.44 m), so that cars could be run to the rest of Europe.
After World War II Moldova became part of the Soviet Union and the rail network reverted to broad gauge.
Given, the Bessarabian rail network was of standard gauge at the onset of Barbarossa, I would expect a similar treatment be afforded as what exists for the Baltic States.
see also:
Report of the People's Commissar of Defense of the USSR to the Central Committee of the All-Union Communist Party of Bolsheviks - I.V. Stalin , Council of People's Commissars of the USSR - V.M. Molotov and the Defense Committee under the Council of People's Commissars of the USSR - K.E. Voroshilov
https://www.alexanderyakovlev.org/fond/ ... oc/1010681
Information of the NKVD of the USSR I.V. Stalin , V.M. Molotov , L.M. Kaganovich on the mobilization preparation of railway transport
https://www.alexanderyakovlev.org/fond/ ... oc/1011363