E21 316: Recaro Seat-Base Adapter - Finally solved!

I'm all for keeping things so they can be converted back to stock later on, but fitting seats with the E21 base-mounts is a nightmare. Once you've overcome the different height on each side and the mounts being too far apart, the seat has to be set low enough to be able to drive the car. I've tried a couple of times and just can't deem a complex two-height setup safe enough to be permanent. The Planted adapters from this post are just too expensive - I don't have £300 to spend on brackets for seats I had lying around so, with regret, the outer [higher] mount has had to be cut out. Gleefully this has done the trick and the passenger seat is now mounted at the perfect height and slides back and forth like it's on ice, so with a nod to retaining originality, this is the first thing anyone wanting to fit sportier seats should do.

Ripping out both mounts gives a blank canvas to put any seat-frame in any position, but a bit more research taught me that the inner mounts by the trans. tunnel can be re-used when fitting upgraded BMW seats, - Recaros, E30 seats etc. - which is what I would fit in future ideally, so they stayed and the outer mount came out to reveal 5" strip of flat surface, the only bit in this area of the floor-pan. Given the choice I would use steel box-section here to raise the flat section up to the same height as the inner mount and do some welding, but I just cant find it anywhere locally in the right size. I got some immense inspiration off this thread on Bimmer-Forums - http://forums.bimmerforums.com/forum/showthread.php?1757170-E30-sport-seats-in-e21 - in particular this guy, who used a block of wood - http://forums.bimmerforums.com/forum/showthread.php?1584670-HSVTurbo-quot-Mac-quot-Build-Thread. Would had been considered originally with the Recaro project, but not ruled solid enough. HSVturbo showed it can work here though and I guess as long as the bracket is bolted well through the floor, the would should be plenty solid as a riser and won't twist about.

It transpired there was a 2x4 type beam leant up in the shed that was pretty much the exact height of the inner seat mount, so I chopped off a 55cm piece of it, to match the full length of the inner mount - I can see the extra PVC-pipe thing works for HSVturbo, but one piece has got to be more secure. I then ran a length of angle-steel from left to right at each end of the inner-mount and bolted it through the existing holes. The angle-steel also sits flush against the front and rear face of the mount and wood-block. Lastly, the angle-steel is bolted through the wood to the floor-pan. Now I have two cross-bars to bolt practically any seat onto, good enough to rival the Planted adapter, well not quite, but it's an inch lower, solid and cost a whopping £6.99 to make. The carpet even fits snugly back over it, with a few slits for the cross-bars to go through.

To mount the Recaro on the cross-bars the base-mounts needed removing entirely. These are held to the sliders some of the strongest rivets I've seen and needed grinding and chiselling out, but thankfully not enough to mess up the holes, which I re-used to mount it with short M4 bolts. For the seatbelt-buckle anchor I just used a short piece of angle-steel, but it will need replacing soon with either a right-angle bracket at least 2.5mm thick, or better still some stalk type buckles from an E30. Some E30 Recaros would go nice with those too...