Here is what I found on the restrictor:
Cylinder Head Oil Restrictor On
1989-95 GM 1.0L Engines
Beware of some confusion on the cylinder head oil restrictor used on 1989-95 GM 1.0L engines. This engine uses hydraulic lash compensators in the cylinder head and the restrictor is used to control the amount of oil directed toward them. The confusion has been the correct location of the restrictor. Apparently some engines have it installed into the cylinder head and some in the cylinder block.
Regardless if the restrictor is screwed into the block or head, it also prevents excessive amounts of oil into the cylinder head area. If the oil control plug (restrictor) is not installed, the additional oil may overwhelm the PCV system and cause oil consumption.
When properly installed, this restrictor, Part #96051574, also acts as an anti-drainback valve and prevents lifter noise at start-up. This engine is made for GM by Suzuki and they also offer this restrictor under Part #11112-73001.
Here is the direct link:
http://www.rebuiltautoengines.com/suzuki-articles.html