It sounds like you've got everything going in the right direction so far.
Did the DEEPsea 8610 come with a manual? Somewhere there should be a register mapping, as well as information about how that modbus is storing its information (this is the 4_BYTE_FLOAT_SWAPPED and such, it's a drop down data type field in Mango). You will need to configure a data point for each of the points you'd like logged, and knowing that data type is the most important thing for turning "1ff0" into whatever its data type is.
I think you're operating with a 2 Byte Int data type (a total guess based on those 2 and 3 values). However, without knowing what kind of data is supposed to be in those fields (which would be supplied by the manual) it is very difficult for me to guess what the actual data type for your board is since I have no idea what those numbers ought mean.
