Jeff,
Steve is correct.

If the originals are cap screws, they should be replaced with like strength
cap screws.  Manufactures watch costs and they don't use stronger (and more
expensive) bolts unless they are needed.

Also, look up the difference between metric Class and SAE Grade for bolt
strength.  This information will help prevent expensive and inconvenient
breakdowns.

If metric bolts are cap screws they are probably Class 12.9 and that will be
written on the top of the head around the edge.  Check to make sure before
you buy.  ETKA shows these to be M12X1.5x20 allen key head bolts.  Be sure
to torque them correctly, which means dry unless indicated different in a
factory (i.e. Bentley) manual.  Make sure the heads of the bolts are the
same height as original.  It is possible, although I don't remember if it is
a problem with the Vanagon, for the heads to hit the clutch disk hub if they
are too tall.  Also, don't buy critical bolts from your local big box store,
buy them from a reputable bolt supplier, either online or locally.  Most
cities of significant size have a quality fastener store.  And also use
quality washers if they were originally present.

Do this and you should be fine.

Ed