In the trade dialogue, almost all the fielders on all MLB teams have a /1B after their position. So most fielders, under "Positions", have C/1B, IF/1B, OF/1B, etc.

(This is a career I am continuing from the 2016 version, and I just moved the save file over to the 2017 folder.)

(I uploaded the mog file named "3" via hightale.)