The Ruskskis may have gotten some Spam, but according to my WW2 vet pappy (may God rest his soul), it was mainly canned pork stew that was about half lard flavored with a single bay leaf. He received a can of this stuff after the war and opened it. He purchased it from a surplus store. The can had both English and Russian writing on it.
Mostly beef. I actually didn’t hear they were getting any spam there. The Soviet specification for canned meat in their ration was beef pieces with bay leaf and salt. Lard was pored on top of the beef before sealing the can to isolate is from residual air which might have stayed in the can so it lasted longer. The specification was submitted to US and it was made under it. Pork wasn’t produced this way in USSR because it was only slightly more than a decade into Stalin’s anti-religious campaign and some troops could refuse to eat it. US actually started to produce canned pork under such specification too and the Soviets accepted it.