Here are some pictures of the surface grinder that followed me home when I retrieved the Index Super 55. Year unknown, but the telephone number for B-S company listed on a sticker on the machine in NJ is of this format: #-####, so that dates it some.
Difference for a surface grinder vs the mill is a very fine surface finish vs the milling marks from the typical milling tools. Assuming that the table is ground square to the wheel and it should be, you will get parallal sides as well and infeeds of .0001" on the wheel.
We have that same machine at the shop and the hydraulics to move the table is it downfall. If you can avoid it, do not take that control block apart.
The controls are fussy and the two are interconnected, turn one knob and you are turning the other to get the proper action back. Be sure to check the ways as lube is critical on this machine.
Did you get the pump and tank with it?
I may have some parts for the control block, if you are interested as the unit was removed a couple years ago on our machine.
I have a manual for a B-S grinder that may be close to the vintage you have. I will try to post it here. It has some information on the hydraulic drive as well. I also have a parts manual for the later Challenger model. There is a lot of commonality between the two designs.
These are sometimes known as the round guard models as opposed to the later machines that had a square guard around the wheel. I have done some work on my B-S grinder, so I may be able to offer some advice if you need to make repairs.