I called Timbren about the bolt length when I installed mine and they assured me that if I really tried, the supplied bolts were correct. I chickened out after aplying a LOT of eblow grease with a long-handled wrench and bought some 1/4" shorter.
Like MC, I don't find them (I only have the rears) to be a problem off-road. They stuff way down. I haven't actually measured under compression, but I believe they squish down to where the OE bumpstop would be - at least they do when there's a load in the back. Plus the bottom isn't abrupt, and the dog appreciates that as he's trying to cope with the bumpy stuff back there.