1.625" diameter tubing is a minimum .118" wall thickness. Anything 1.5" diameter and smaller is a minimum .108" thickness. These specs are for a mild steel 25.4 chassis that will cert 7.50. Pretty current specs as I just got the paperwork from sfi last week.

Back to the OP. If that chassis was built with .120" wall tubing it may not pass cert with the amount of rust shown. If it was built with .134" wall tubing you should be good if you add/correct the chassis as needed for current sfi specs. Beep