Hi Adrian,
sorry , i m not sure i understand what you mean
do you mean the round tube at the bottom ?
are your back stays welded into the bottom corners or bolted?
when i got my rear tub i basically placed it into position & built my rear chassis in conjunction of the tub shape/dimensions,
unless i,m getting too old & losing my memory
i used some photos that you posted as a guide to what i did, i,m confused
ahh, is the prob with your new chassis? ( i think the penny has just dropped into place) not meaning the chassis is a prob,
cheers
andy