Here we go again. Some well-intended but questionable info so far.
The MK2 and Mk3 platters were the same platter; no difference. It is a very good platter, but not as good as the heavier Mk4/TNT platters. The difference between the Mk2 and Mk3 tables was the stainless steel chassis and acrylic top plate of the Mk3. The difference in sound between the Mk2/3 chassis and the one you have (Jr.) is not nearly as significant as the difference between the Jr. frosted and Mk2 platter. So, you are in good shape as far as that goes. Personally, I would leave the chassis alone and add a SDS. The improvement will be greater than that wrought by adding the SAMA, or even the MK4 platter. A no-brainer IMO. A used SDS and a Denon 103R (if you have the gain) for $1000, and you will be in a different sonic league.
The MK2 and Mk3 platters were the same platter; no difference. It is a very good platter, but not as good as the heavier Mk4/TNT platters. The difference between the Mk2 and Mk3 tables was the stainless steel chassis and acrylic top plate of the Mk3. The difference in sound between the Mk2/3 chassis and the one you have (Jr.) is not nearly as significant as the difference between the Jr. frosted and Mk2 platter. So, you are in good shape as far as that goes. Personally, I would leave the chassis alone and add a SDS. The improvement will be greater than that wrought by adding the SAMA, or even the MK4 platter. A no-brainer IMO. A used SDS and a Denon 103R (if you have the gain) for $1000, and you will be in a different sonic league.