Maybe this is an old topic but it is still interesting. Your display of a soldier of the former Bulgarian Peoples Army (1970) is nice but it is not correct.
The gas mask, PG-1, came in service in the Bulgarian army in the first years after the fall of the communism in 1990. I think that the BSS-MO-4U or SR-1 gas mask should fit better to your display. The SS-MO-4U and SR-1 gas masks are the Bulgarian clones of the Soviet SchM-41 M gas mask. Bulgaria exported these gas masks to all the former East Block countries. The SS-MO-4U gas mask is very easy to find.
The camouflage helmet cover is also interesting. As far as I know this version of the camouflage pattern "Splinter" was introduced in the late 1960's (Not to be confused with the earlier M1953 or the "frog" pattern). It was devolved for Bulgarian paratroopers. Later it was also introduced by border troops.