Hi,
On C70 I put Volvo tower brace. I had winter tires on at the time so can't speak
to how much/little it helped. Note when installing it, you should jack up front of
car so wheels off ground, tighten bolts (that are on shock towers holding bar ends)
then lower to "pre tension" the bar.

On C70 Coupe and 850s it is possible to get the u-brace fron C70 convertible and mount
it under frame for additional supprt. need to get the bolts (longer than standard) with
it. Buddy did so on his 850, reported he could feel difference.

Hope this helps,
Carl