Does this new master cylinder look correct?

[Toro]

Take a look at the photos comparing the original MC on my 72 with power brakes, to the new AC Delco 18M1036 I just ordered. Should I be concerned that the rear reservoir is so much smaller? The bore size/depth, fittings, etc are all the same. I didn't expect to find an exact match, but just wanted to double check. Also, any ideas what that 5/16 bolt is for in the bottom of the front on the original? Never noticed it until today when I pulled it off.