I'm of the same opinion that some others here are of, and that's that I can do a very good job making my own cross-members. I didn't come to this conclusion for the sake of saving dollars, I came to it because I like to place the cross-members where I want them and at the height's I need, not like some cookie cut outfit thought I should.
We just finished our 1933 Ford Tudor sedan chassis, and we went whole hog on the thing. I started with a pair of stamped frame rails from ASG, and the rest was our own design. I boxed both sides of the frame completely, then made the rear spreader bar, along with a temporary front spreader to hold the frame rails at the right distance away. The mid section was all done in round tubing, why round, because it has the highest strength and look very nice when you do it right. Most mid-section kits use a top and lower section that is welded into the frame rails on each side then tied together in the middle. While this may be a good set-up, I had Way to many coolers, filters accumulators and so forth to waste all that room with mid-section bracing. We made all our own straight and bent center section pieces in house and while we did not double brace the center section, it is more then stiff enough. Truth is, those double stacked center section, just cause to much commotion when it comes time to run exhaust systems, oil, inter-cooler coolers and everything else that is needed for a modern day street car.
While this worked out for us, I would not recommend the average guy or garage to tackle such a feat. You need to have the proper tools and equipment like Tube benders, welders, frame table and so on. But the end result is a truly custom chassis that fits your needs. If you think you have what it takes to do just such a move, then by all means go for it, the results are worth all the time and trouble involved. Good Luck