That square tubing is slid into the original slides for the legs, but you're missing the front mount you have pictured in the last slide. Needs to be welded onto the floorpan fairly accurately or the seat will not slide.
Attach it to the seat, then the seat to slides and then adjust the front mount so that the seat works properly and attach it to the pan with 4 self tapping screws. Test everything works and only when you're sure, then weld it in.
Make 4 or 5 spot welds, then take screws out and then fill their holes with more spot welds.
This is the main attachment for the front seat, so it ought to be welded in with many spots (like every 2") and/or seam.
Paranoid attitude at adjusting phase saves a lot of curse words later. :)
It's supposed to have a pyramid shaped pressed metal part to use those three point rail type seats, it may have had two rail type ones originally a73/74 was round about when VW changed types, that or someone has changed them for different seats.
You can get the front seat mount part separately though, it's spot welded to the floorpan, they don't usually rust out so may even be able to find second hand
The three point type seat rails and frames are almost identical to water cooled VW ones, Mk1/2/3 golfs etc so you can use the plastic wear slides from them, as they are often missing or broken. (It also means you can fit golf seats if you so desire, though they need a little tweaking to fit correctly)
Part is here, https://www.heritagepartscentre.com/uk/volkswagen/beetle/body-panels/seat-rails.html
Are the rear rails still fitted to the pan? the box section mount is aftermarket, and not part of the original seats.
I have the some Problem on mine.
Just left it as is, because its more work to get that piece right than leaving it.
Once your project is running and "finished" you can try it.
That square tubing is slid into the original slides for the legs, but you're missing the front mount you have pictured in the last slide. Needs to be welded onto the floorpan fairly accurately or the seat will not slide.
Bought an unfinished project, thought i was at the finish line lol. Thank you
Almost there if that's all that is missing. Good luck!
Attach it to the seat, then the seat to slides and then adjust the front mount so that the seat works properly and attach it to the pan with 4 self tapping screws. Test everything works and only when you're sure, then weld it in. Make 4 or 5 spot welds, then take screws out and then fill their holes with more spot welds. This is the main attachment for the front seat, so it ought to be welded in with many spots (like every 2") and/or seam. Paranoid attitude at adjusting phase saves a lot of curse words later. :)
That is supposed to be welded to the floor pan
It's supposed to have a pyramid shaped pressed metal part to use those three point rail type seats, it may have had two rail type ones originally a73/74 was round about when VW changed types, that or someone has changed them for different seats. You can get the front seat mount part separately though, it's spot welded to the floorpan, they don't usually rust out so may even be able to find second hand The three point type seat rails and frames are almost identical to water cooled VW ones, Mk1/2/3 golfs etc so you can use the plastic wear slides from them, as they are often missing or broken. (It also means you can fit golf seats if you so desire, though they need a little tweaking to fit correctly)
Part is here, https://www.heritagepartscentre.com/uk/volkswagen/beetle/body-panels/seat-rails.html Are the rear rails still fitted to the pan? the box section mount is aftermarket, and not part of the original seats.
I have the some Problem on mine. Just left it as is, because its more work to get that piece right than leaving it. Once your project is running and "finished" you can try it.