I think the wheel base is long and the tires are too grippy for skid steer like a Bobcat. The early Bobcat's had really short wheelbase; shorter in length than width. Now they have increased the wheelbase for stability, but have 60HP engines to power turning. Since you are using the blade and out-riggers to stabilize while digging, the wheels are just for transport. I would consider moving the wheels much closer together.
Use counterbalance valves for downhill speed control; they are available to mount directly on motor depending on motor make/model.
Will you disconnect motors for towing?
I am 55 '' wide and 53 '' wheelbase.
So I proportionally a little longer than the bobcat that would have 44 '' of wheelbase for this width.
This vehicle will not work on pavement, often gravel and dirt, it's easy. Especially since the weight on the rear wheels is lower than the weight on the front wheels, the rear wheels will be easy to derail.
The machine will circulate in the wood, so I wanted it not too late pouring when the terrain is uneven.
For engine power and traction, the Bobcat 60hp is more than 6000lbs without load in the bucket, and my excavator will weigh less than 2400lbs, and will have a lower movement speed, so much torque compared to the weight of the excavator.
I have not seen these motor with valves, are they expensive? My method of 'braking' is not perfect but very affordable.
The excavator tires would not ride well on the road, and the weight on the tow bar would be much too high. It's trailer tires that will be on the ground with trailer hubs, the 4 wheels of the excavator will be 6 '' to 10 '' in the air.