The piece of pipe you are after is made up of two pieces, the piece that is y shaped is one and the piece that goes over the axle is another. The latter piece does come up on Ebay sometimes but I have not seem the y piece ever listed. This piece could probably me made up by an exhaust specalist but the piece over the rear axle would have to be made very accuratly.
This is the ROVER 75 version https://www.ebay.co.uk/itm/184539769...Bk9SR4iWtY2MYQ I suppose this could be used on a ZTT as is or modified by removing the silencer.


Steve