I got one of these mate:
https://www.ebay.co.uk/itm/224082800190
Couldn't separate the mid section pipe from the downpipes and it was in good nic so I cut it with my angle grinder and used the included joint (it's like a sleeve) to connect the backbox to it. Easy job - the only pita is the rubber mounts - I cut the old ones off and used some WD40 to get the new ones on. Use your jack to lift the backbox into position.