From my personal experience, this particular set of braces does not make the ride more rough at all. I am speaking about my '90 745 wagon (which is the first car I ever owned :-) ..take into account that a modern Toyota ride is probably more smooth, and I do not know if you managed your 740 to this level).

The upper brace I installed connects the strut mounts. What I learned from reviews, is that another type of upper braces which connects to the back side wall of the engine compartment with its one end is prone to transmit the vibrations to the salon. Another note is that all the braces probably make your engine slightly less accessible for repairs/checkups.

I have installed the braces after my friend showed me his '89 745 sedan, where he mounted a home-made lower brace. He mentioned that when going mountain roads with many twists, he noticed the difference.

Best regards,
Wolandir