From @idratherbstacking on IG or William Silver on FB.
If you read the All Engelhard Foster page, there is a fair amount of speculation about who exactly made the poured bars. This information below sheds some light on the issue but doesn't have a definitive answer who made them.
There were various coin companies that operated in Walla Walla, Washington from the late 1950s through the 1980s. A incomplete list includes:
The people that were involved:
Timeline of advertisements of poured Foster bars: