Unfortunately I've been struggling to get up to work on the mini recently due to work and family commitments, but I have managed to get the rear end pretty much finished off. I opted for a Magnum rear valance mainly due to it being less than half the price of a heritage panel. It's the first non-heritage or M-Machine panel I've gone for and although the steel is noticeably thinner, the fit was more than acceptable and it lined up well. Along with the valance I bought M-Machines rear valance closing panel/subframe mount panel.
I didn't take any pictures of it all clamped up but it all fitted together well. Here's the O/S closing panel tacked in place ans spot welded to the valance. Note the ropey seam weld along rear of the wheel arch - I couldn't get the spot welder in there to weld all three panels together so tried to run a seam along the top, not the prettiest but it'll do for now! One of the holes for rear subframe bolt is unavoidably slightly out so that'll need re-drilling later on too.

And fully seam welded in place.

In future I'll also drill holes in the closing panel and plug weld it to the boot floor, not sure why I didn't this time, I think I just got a but of tunnel vision and overlooked it
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Here's the other one welded on too along with the valance.

And a shot from underneath after welding the valance on. It was all nice and easy due to being nice new steel so the spot welder took really well to it, it was just a slow process as the duty cycle only allows 2 welds per minute. I also made sure to crank it up as it was essentially welding a 3 panel sandwich.

The only bit I'm not happy with is the the very ends of closing panels not mating with the end of the valance as you can see. I put this down to a slightly incorrect profile shape on the M-Machine closing panel but it won't be too much work to quickly knock up a piece to fill it in.