I needed to make the set-down position adjustment on a SL-1300, and I too did not find an adjustment screw, per se. What I did find was a silvery arm that moves under the 'adjustment screw hole' as the tone arm is rotated. If you hold this arm motionless, while gently forcing the tone arm past the point of resistance, inward or outward, the set-down point is adjusted inward or outward. There is a slot in the middle of this arm, suggesting a procedure of holding a screwdriver in the slot to hold the arm motionless.
The rearward edge of this arm is close to, but not past, the rearward side of the adjustment screw hole, when this adjustment is close to correct. If the arm is rotated a fraction of an inch inward, the slot in the arm becomes visible under the hole. If the arm is rotated as much an an inch inward, the 'front edge' of the arm moves past the adjustment hole, and is no longer visible.
I found the adjustment hard to complete--it was always too far in or too far out--until I tried an alternate adjustment method. Instead of inserting the screwdriver into the slot, I immobilized the arm by holding the screwdriver against the rear edge or front edge of the arm. In this way I found I could successfully make finer adjustments.
BTW, the tone arm rest is half-missing on this unit, and I found one can instantly destroy this adjustment by moving the tonearm outward past the rest position.... This discovery led me to loosen and rotate the tone arm rest so the surviving 1/2 of it was in position to keep the tonearm from moving outward.