If you find a copy of H. T. Crittenden's The Maine Scenic Route there is an appendix with scale drawings of many of the SR&RL engines and cars. #9 and #21 are in there in their most modern form.
This may vary with edition. I have a hardbound copy that only has drawings for #1 and #5. I would urge anyone who purchases a copy to get a good look at it first.
-John
The copy I have has drawings for LR&HS "James Wyman" (SR&RL 16), SR&RL Nos. 8, 9, 10, 16 (rebuilt), 18, 20, 21, 22, 23, and 24. Also, RPO No. 6, Combines 14 and 15, Coach 22, Parlor 9, and Caboose 556. Small but readable.