That looks like one off hand built for that specific chassis. Find a Rod Shop with a tubing bender. The Wizzard
Like he said. Huth tube bender: try your local muffler shop. They have heavy tubing in stock, will bend to your specs. But take a clothes hanger bent to the center of shape of the proposed 'cross member'. Most muffler shops stock thicker wall tube than "Muffler Moly"...and can/will bend 'to suit'.
I was thinking this was some sort of manufactured kit. Hmmm. I really didn't want to have to get creative ha
Well thats no fun!!!!!! Years ago the rod shop I used to go to had a company that made stock panels bend up a bunch of X members. Then a guy had to cut and fit to there need.
Not quiet the style you ask about but Progressive Automotive out of Ohio uses a tubular cross member in their chassis. HRP Here
Google Tubular X member. You get some wired crap like tennis shoes with an X something but you get the link for the Google photos of Tubular X members plus several links.
The Jalopy Journal
