Two holes does sound a bit restrictive is there any chance of getting 3 x 3mm in?
By way of comparrison my 2" Fowler has a 2" stroke but larger 1.375" bore which works out about double the area of your 1" bore and ports are double at 1" x 1/8" , that has six 1/8" holes, you do have to pack them in a bit tightly though.

And another tightly spaced set of holes
