Charlie - Mini Mk3

[Miniac]

I'd look into using some rectangular tubing such as a 40x20mm by the applicable length and the drill it and mount some Rivnuts into it for the seats to bolt up to, I'd then have a length on 3-4mm flat bar twisted through a 90degree to mount into the original mini brackets on the crossmember and have it welded onto the rectangular tube to complete the bracket ready for paint and fitment.