Here's what I've been able to determine looking at the manuals and doing other searches.
The SVT-1540HE can be configured as either two separate cabs, one 4x10 and one 1x15, or as one full range cab. As separate cabs, each cab is rated at 4 ohms; as one full range cab, the rating is 8 ohms. The owner's manual does not state the power handling capacity. In my search, I've seen it rated at 400 watts, 8 ohms; so presumably the 400 watts applies to the full range mode. I also saw a posting stating that in separate mode, each section was rated at 200 watts, 4 ohms; but I don't know how reliable that is. I've seen other ratings posted as well, and have not been able to find power ratings from a reliable source.
Does the cabinet have power ratings stamped on the back?
The left and right speaker outputs of the 2001RB will each deliver 360 watts into 4 ohm loads. The bridge and biamp modes apparently require 4-lead speakon cables,and the manual suggests that those modes are specifically designed to work with GK RBH cabs.
Thus, if you want to use this amp with this cab, my guess is you'll probably want to plug one channel into the 4x10 input and the the second channel into the 1x15 input. However, personally I don't think it's a great idea to run a full range signal into a 1x15. Although the manual is unclear on this, the specs suggest that you could just plug the left speaker out into the full range input of the 1540 and you would be providing 240 watts into an 8 ohm load. However, as suggested above, the full range input of the 1540 is probably going to be underpowered with just 240 watts.
I think this head and this cab, both of which seem underpowered, are somewhat mismatched.
The head would probably work fine with two 4 ohm 4x10s rated at no more than 360 watts.
I'm no expert, so don't take the above as 100% accurate. But that's my guess at what you are looking at.
[Added] Ok; in reading through the manual further, if you use a 2-lead speakon cable, wired as shown in the manual, and you only use the left speakon speaker output (and adjusting the level outputs as described in the manual), then you can use bridged mode with non GK cabs. So, in bridged mode, the amp will deliver 1080 watts into a 4 ohm load or 650 watts into an 8 ohm load. Thus in bridged mode this amp should be matched up fine with the 1540 using the full range 8 ohm input.
Again, that's my guess.