My design with alot of research.Looked at cpl thousand pics of chassis,lots measurements a calculations and even scaled a cpl of 1/16 models of old FEDS.May seem stupid but those things are very accurate reproductions and scaled to be almost exact copy. Half dozen or so full scale drawings also.
Will I change a few things on next car yes,will it be a lot of things nope. How well did I do? Looks good ,omly some runs will tell. Would using someone elses design drawing and modifing to suit my wants have been better idea,heck probably. If you order a SFI spec you get very detailed drawing of whats acceptable and safe. Very well spent $35.
You are already off to good start researching it. If you do build be prepared for long hours in shop(a plus),changes will be made, cost of tubing and tooling to be more than expect.Price of satisfaction of having done it yourself is hard to place on it.