[Alpines] Head gasket

[Moto]

Hello
    I am vintage racing a series II alpine
with a bored and stroked 1725 engine
it has 12.5/1 compression
with 7/16s  head studs
I keep on blowing head gaskets  in to the watre jackets
I am using a custom made copper head gasket  by cometic
the motor is 0 decked and the head is straight

Any suggestions on head gaskets or different sealers to use
I was thinking of O ringing the block next
I only  got 2  races at NJ  this weekend before it started  Leak
into cylinder 2

Thanks
  Rocco