The only lock out bobcat have is to block the pedals so it will not lift or tilt, the park brake stops the steering levers move the machine.Yes, the stock 743 will move if you bump the R/L wheel-drive levers, but I have never found it to be an issue. The levers have to be bumped a lot to get much movement. I'm not saying I have never bumped them (or hooked a shirt-sleeve on one), but it isn't a real problem.
Give me a few days, i'll try and get some pictures of the centering system. You have the main part that is needed with the holes cut in it. It uses a spring and stops to hold it in neutral.
Can you look up my profile and send me an email? i can hopefully get you a copy of a 743 manual that will show how it all works.