Slapper bars are easy to make to bolt under leaf springs. I just had to buy slightly longer U bolts
This is a vid from back in the day. But you can see the slapper bar on the passenger side doing its stuff.
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw