The technical term for a piece of threaded hardware that has LH threads on one side and RH threads on the other is a Turnbuckle. What you have however looks like some sort of custom machined component. I think if it is bolted down well you shouldn't need to concern yourself with being able to tension the unit...if anything it would put undue strain on your spring towers. I have heard the opposite....the supra is so stiff (and the suspension forces aren't being driven into the spring towers), that tower braces do very little to improve matters. I suppose if you were using the cross bar to triangulate the towers to the firewall or a cage than you might see some benefit, but just tying the two towers together won't do much IMO. I know you see it all the time on Hondas, but they are also running a much different suspension configuration than we are, and their frames aren't anywhere near as stiff.
SG in NE