The very early 28 Cowl, in addition to the cowl welting mentioned by Tom, also use different hood sills to match the cowl; the date stamp on the gas tank did not start until around May 1928; the hole for the starter rod is in a different position to accomodate the off set starter rod, later the hole was moved as the second generation starter rod was made straight. When the brake handle was moved to the front of the gear shift the first early cowls had a plate using screws to hold it in place to cover the hole for the left hand brake, later the plate was rivited in place; when the old cowls were used up the new cowls elimanted this hole.
Ron