I filled my ute mounts with windscreen urethane and it does make a big difference to stiffness, however it does not make them any stronger. What happens if you drive the car hard is that LHS (drivers side for you yanks) side of the engine tries to lift up under hard accel and eventually succeeds by ripping the rubber in half. There is no good solution to this bar replacing the mounts with a different design.
Here are some pics :
Should be pretty easy to fab up something similar. Key point is that they are retained by steel, so the rubber can wear out and your engine won't come out through your bonnet like it will with the stockers (or even mazdaspeed miata ones).
I broke 3 ute mounts with 80hp and one skyline mount with 150hp. Hence the 400hp ute is reinforced, but the corolla arms I used are heavy and ugly and in the way. They need to go and this is the solution.
I don't have this in my possession yet, but these should be shipped to NZ at some point in the nearish future. The will allow me more room to use a larger filter and/or adapters and what have you for oil cooling if I end up needing it.