Once the stringers were in place, I marked their location on the bulkheads.
Putting a dado blade in the table saw, and setting it to 1/4 in., the grooves were cut. The cuts were 1/4 in. deep which when the stringers were inserted left 1/4 in. sticking out.
Then the bulkheads were reinserted and the stringers put into the grooves.
Nice and straight.