re: question about a pro street frame
Unless you are really into designing your own rear frame section, you should look into purchasing a pre engineered system from Art Morrison or Chris Alston or many others. If you are going to do it yourself, there are many things to consider and it would be tough to cover in a forum like this. Some of the main points to shoot for are when the vehicle is at ride height are...
The lower 4-link bars should be parallel to the ground to start with.
The coil-over units should have about 60-70% of the travel available for bump travel (compression) with the rest for droop travel.
Mount the coil-overs as far outboard on the axle as possible and angle them inboard at the top about 10-20 degrees.
Have enough clearance over the rear axle so you can run exhaust and still have more than enough clearance so when the suspension is at full bump, nothing will hit.
Install a panhard bar if the car is for street use, and make it as long as practical. The longer the better and attach it to the frame on the right side. Make the mounts and the bar beefy. DO NOT use the panhard bars that bolt to the third member of a Ford axle. Longer bars are much better even with the extra effort to get one in. Make it parallel to the ground at ride height and roughly centered on the rear axle housing. Do this step even if using an aftermarket rear clip!
Stay away from any Heim joints in the linkages and go with Urethane style ends.
Make the connection to the stock frame very beefy and/or add a roll cage to tie the rear frame into the rest of the vehicle.
It is great fun to build a set-up like this, but do some reading up on the subject before diving in. Chris Alston has an excellent book on chassis construction and set up that you might want to check out. Let me know if you have more questions!