91PA, the GP radiator core support is totally different, and heavily reinforced. Doing that to an H body is very bad advice.
It'* also not necessary. There are plenty of ways to get the same result by improving/changing the stock mounts.
I would caution ANYONE with an H body not to install the GP upper dogbone braces without some very creative support in place (which probably isn't possible due to the hood structure and large radiator).
The GP has the dogbones because they have a different subframe. They can't run lower mounts where we do.
In addition, that solid RR dogbone is a VERY bad idea. The stresses applied by the drivetrain have no buffer. You're going to break your differential housing eventually. And have to live with a helluvalot of vibration.