For those that are interested in Delkevic downpipes, this is how my recent purchase worked out.
The advantage of the separate downpipes and collector design is clear, they fit in a surprisingly small box. In the absence of any included instructions I assembled them off the bike since those springs that hold the headers in the collector looked as if they'd need a lot of force. In fact, they need an amazing stretch... way beyond the elastic limit, i.e. they don't return to their original length once they've been pulled far enough to hook the parts together.
I then offered the pipes up to the bike, locating the downpipes into the cylinder head ports and loosely bolting the rear to the support under the footpeg, and found the fit was not all it could be.
For a start the headers run noticeably closer to the frame where they go past the steel coolant pipe. For most people that wouldn't be a problem, but I'd had to reposition the coolant pipe a bit forward to suit an aftermarket radiator and it was now stopping the left hand header from seating properly. After changing the spacer for the coolant pipe I was then able to get the headers to seal against the cylinder head ok.
Well... ok until I tightened up the rear bolt. The collector wanted to be lower, further forward and to the left of where it should be, with it forced into position by the bolt the strain was enough to cause the downpipes to leak at the head. Removing the rear bolt completely solved that, but I wasn't happy with the entire system supported on the header clamps and the strap hanger for the silencer... and suspected an MOT inspector wouldn't be either.
After an email exchange with Delkevic they advised that the springs are attached afterwards and the downpipes shouldn't be seated fully into the collector. So, after dismantling and assembling again, the fit is better but still not good. I've had to include a spacer of 5mm between the collector bracket and the footpeg support to reduce the sideways strain on the headers, the pipes are about 1 cm from being fully seated into the collector, the springs are about 3x their natural length… it's a bit noisy and I can't work out if it's still leaking at a joint somewhere.
Since Motad downpipes are accurately made so they bolt straight on and are less expensive, I now wish I'd gone back to them rather than experimenting.
Still, at least you don't need to make the same mistake.