It appears reading comprehension has left the building(except for Rick, he got it).
Chappy has a VMC SPYDER. Not a Beck Spyder. Not a Speedster of any ilk.
The 2" chromoly tube runs on the outside of the seats, just inside the inner wheel well. You'll see either rivets for early cars or self-tapping screws for later cars attaching the aluminum floor through the fiberglass and into the frame tubes.
I jack mine up there, in the front, behind the beam. I'll put jackstands under the lower beam tube. The beam sticks out a little beyond the frame.
In the rear, I jack up the frame tube just behind the firewall and fiberglass bodywork that wraps underneath. That spot is just in front of the rear wheels. Don't jack too far back, the tube angles upward and you don't want the jack to slip.
I've also put the jack under the exhaust under the rear crossmember. There I used a 4 to 6 inch long piece of 4 x 4 under the trans mount. If you have a low jack you can also get the crossmember under the engine/trans. They're all 0.120" wall tubing, very sturdy.