I used 2x6 box tube on my most recent chassis build and will do it again as it gave me a good bit of room to run exhaust and mufflers inside the frame rails. One 20 foot bar is plenty.
I am looking at using the front ends from S-10 pickups as they are close to the same as a Nova and a lot more available..cut it off of the donor chassis just behind the lower control arm mounting points and use it like one would use a Nova front end. while you are getting the front cut the rear frame clip out of the s-10 just about 6-8 inches ahead of the front sspring mount..then connect the 2 pieces with your sq tube..When you are cutting clips out of a donor leave enough trim so you can fit the tubing to the clips..
The major deal with the S-10 chassis is that the stock configuration has a lot of humps and bumps and wiggles to it that make it hard to use for a rod project..Doing what I outline makes it much more usable..
I have tried most all of it and now do what is known to work..