refrence help

I need a reference to a company or companies who can build me a rear suspension ( 4 link) for my specks. The original car has a rear independent suspension and was a fwd. I want to go straight axel.

Are there companies who offer basic systems with the ability to be modified for custom needs?

I will make the adapting portion to attach the system to but I want to reduce the possibilities of problems.

Again this has never been a rwd and I do not want to cut or mess with too much of the unibody. . There are large and very strong rear mounting points based on large strut towers and lower a arm mounts. My point is the uni-body is already fairly strong and I would prefer to add to it instead of butcher it.

I still have vague numbers but figured there may be some who can help before I start figuring out what suspension system from what car to base it on. Thinking of going firebird but really not 100% sure.

Thanks for any help, creative criticism or ideas.