I have a 518 behind my Hemi. The 518 itself won't slow the car down with the exception of it's additional weight. Little or no impact on straight line performance.

As to the cross member, that one suffers from the same problem mine has. The mount is forward of the cross member which puts it in a leverage situation trying to twist the entire assembly. These 518s are heavy.

I intend to make a new cross member where the mount is centered under the cross member. There are 3 mounting holes on the tranny, so making a plate to position the mount directly under the cross member shouldn't be that big a deal.

Personally, I love the 518 and feel it is worth the trouble to fit it in my Cuda. Now, trying to get it in an A body might be a different matter.