A deck of playing cards will make hundreds of backplate gaskets.  I usually use lapping compound on the back plate and crank case.  When I do that I only use gasket  goop/paste or what ever it is from a tube.  No other material needed.  Now socket head screws come from my local ACE Hardware,  but now RTL Fasteners now has socket head bolts.  And as I stated head gaskets from diet Pepsi cans.