Hey Rob, the levers on the right are the drive/brake system. Left lever left track, right lever right track (front of the car body is the idler tumbler, rear is the drive tumbler with the sprocket and drive chain, it can be confusing when you're facing the opposite way!!). I haven't ran ours for a few months, but I believe lever forward is the brake and lever rearward is drive. The levers control a meshing gear plus the brake shoe.
When braking there is a hydraulic cylinder that disengages the meshing gear while simultaneously applying the brake to lock the track. Sometimes you need to use the forward/reverse lever (on the left side of the seat) to release any binding that might be on the meshing gear, same goes for getting it back into gear (sometimes the meshing gear doesn't "mesh" and needs a little movement to do so). Operation for drive is just the opposite, the hydraulic cylinder releases the brake shoe and engages the meshing gear.
I don't recall what the hydraulic source is for these cylinders, but I think it comes off of the swing system, the valve bank in the center of the machine. On ours, we had to have the brake shoes relined ($100 a shoe), due to old, cracked, missing shoe liner. We found the braking system wasn't working so the track would still move while in neutral causing it to turn very slowly or not at all.
As far as high/low. The original lever for this is the lever forward of the throttle lever (upper left of the control console). This lever is actually a hydraulic pump which is plumbed through the center of the pivot point to the underside of the machine, which in turn throws a single valve for high or low. The difference is either high pressure to both tracks in low (top speed of about 1mph), or high pressure to the left track and residual pressure to the right track in high (top speed of about 2mph). SLOW either way!! Going up an incline or long straight paths in high will tend to have a right turn due to just residual pressure going to the right track.
On ours, the lever has been disabled (probably long before we got it). There is a rod sticking out of the turret in the rear connected directly to the high/low valve. It works by either pushing or pulling on this rod. You have to get off and do this manually!! Can be a pain! Out is low, in is high. I used the pneumonic of out has an "o" hence low and in has an "i" hence high.
There is definitely a learning curve on getting used to the turning system. If I haven't been running it for a while, it still takes a few times of doing it the wrong way to remember the correct way. If there is a problem you would have to get under it, remove the belly pans, and check out what's going on. After working on ours, I found there are several mechanisms working together that all need to be working and adjusted correctly as well.
Hope all this helps. Hope you figure out the Hein as well!
