I think you could use those manifolds on a street/strip car especially for something set up more for the stock classes.
As for custom headers It's not as hard as it seems. I have made several sets but I use solid styreen rod, working on the shape of each pipe individually. I find that while solder is easy to bend it doesn't hold its shape. You should give it a try. I won't post examples but if you would like to see some or have questions let me know and we can discuss it through PMs.