Just my own opinion, but the basic original style 55-57 suspension makes a pretty good basis for a street driven car, and can be upgraded to just about any level a person would wish. The Tri-5s are about the most heavily supported classic cars on the market and the pieces are readily available. Unless your frame has been butchered beyond repair, I would say it is likely the most cost effective to go back to a stock or hi-bred configuration. I'm guessing from the way you asked the question about swapping the Cutlass pieces that you have never done a suspension swap. Such swaps need to be completely researched and well laid out to be successful. If you are not capable of doing the set-up and welding yourself you'll find that having it professionally done will be more expensive than just going back to stock pieces (even if you have to replace the frame). Good luck on your project and let us know what you come up with.