I have not ran 357 in a SDB in 5 years and for the life of me I can't remember if there is a spacer for the die or not..
The dies for 38/357 are the same ones..so how do you adjust for the extra length of the 357?
It's been a while since I had one but it appears you just turn all the dies down about .135" except the sizing die. It should be down all the way for both rounds.
Like most sets the dies are the same for both rounds.
Spacers would actually go for swapping the other way since the dies need to be higher for 38 Special. The issue is you need to unscrew the dies to add them and I always just adjust the dies since there is fine tuning to be done anyways.
You could remove the powder dump and measure the height of the dies to save some time later if desired.