Which is why on our replacement frames the mounting points for the top bolt of the rear suspension have been slightly extended towards the rear, and which is why the Andover Norton luggage rack has the connection to the "Z"-plate, thus suspending the whole package and using the rear frame loop only as a stabilizer sideways. See
http://www.andover-norton.co.uk/Accessories.htm
The rear frame loop was designed to only keep the rear mudguard and tail light from dropping into the road, not for taking heavy loads.
Joe/Andover Norton