A-518 Who has put one in an A-boby

I have a 69 Cuda small block w/727, Just got it on the road. I'm thinking already about putting something with an overdrive in. Motor is probly making around 430 to 450 hp. Anybody using a A-518 and how much trouble are they to switch to. And also will they hold up, will see some strip time along with highway driving. Thanks for any input. Tom