Help identify the author of the picture in 1966
 

Good day!
Found in the collection of my father ( an artist Hsar Gassiev ) painting " Portrait of Nick Gintovt " 1966 . Signed recalls " um . " Father in the 60's was a friend of Moscow artists , the collection is also Yakovlev , Piatnitsky , Kurochkin, later Chubarov . The author of this painting could not identify .
Thank you for your help.
Our collection site www.gassiev.ru

addition
 

Of all who came into his head with the initials "GM" - Mikhail Grobman.
But it is very unlike.
Can such a funny stilizovany.
Posted Grobmanu the site until there is no answer.

ps.
Gintovt - Moscow collector, and party-goer, was friends with artists 60s.
In the 70 committed suicide.