The inspectors are getting pretty cluey these days, which is my fear. Maybe it's worth going through and getting the car engineered with the C4 suspension; it would be a very expensive exercise but the car would be better for it.
My reasoning for aftermarket arms on the C3 chassis was that they can easily be removed when it comes time for inspection. For better of for worse...
But how could a c4 based frame not pass a visual inspection, I mean it's not like aftermarket suspension, it's been tested in the usa and meets and dot standards set. I would think they would much rather see that then some aftermarket piece.
Just get a cheaper 4,000.00 frame rather then a tube frame. Have it setup for mono-springs. In the end you would have a far superior driving car without the bandaids that marginally make a c3 suspension better. I have looked into both aspects for my 82 such as steeroids, better sway bars, better springs, after-market rear suspension pieces. But in the end it approaches the cost of a c4 frame.
I have yet to see any of these companies do any real world testing to prove how there stuff compares to stock and would really love to see them build a complete car and see how it stacks up against a stock c4 suspension frame both in cost and performance.
I just think companies like sharkbite/steeriods/ etc. etc are geared towards looks verses eliminating the crappy c3 suspension bad traits. I can see a rack improving the steering but then it still has the original bumpsteer issues along with flexing issues.
way I see it you can take your rolling c3 frame if rust free and get a good 1500 for it use that money to buy a ragged out c4 donor then just save up for the frame. You could use the c4 drivetrain for better all around driveability and economy and better availabilty of performance add-ons and in the end up with a real world c3 that has the great looks but awesome c4 handling without guessing will this help my car or is it more for looks.
You could even part out stuff from the c4 to put towards your frame, I just think it is pointless to dump tons of money into a 30 y/o frame and suspension when the solution to all the problems is so simple.