What was the Soviet 1939 physical output (GDP) valued directly in US 1939 dollars as a precent of US GDP per capita. The same for Soviet industrial output.
I don't touch on GDP specifically, but this is an extensive comparison of the USSR and USA economies which might be of interest.
The most recent Maddison project estimates for the 1939 GDP per Capita (in 1990 Geary-Khamis dollar eqivalents) of the Soviet Union and the United States are $2237 and $6561 respectively. This would make the Soviet figure just about 34% of the one for the US.
As u/Georgy_K_Zhukov's post implies however, a direct comparison of the 1939 figure might not give a complete picture of the capacity of their respective economies.
edit: Also note that GDP is not a measure of purely physical or industrial output. It is an attempt at estimating the value of all goods and services produced within an economy.