O.K. Heres the deal: I've done one, and its not for the fainthearted.
The first thing to do it properly the whole of the interior, front screen, front subframe, boot trim, wiper assembly, instruments, dash loom and fuel tank have to come out. The ideal is to have a bare shell, with headlining out: you'll be doing a lot of welding in the car, and the fumes get into any interior materials, and takes a long time to go: great for that authentic Cut and Shut smell.
Parts you will need (all RHD) Pedal box, bulkhead, dashtop (tres £££), lower dash trims, outer steering column with lock, loom, master cylinder plumbing, brake pipes from master cylinder, front subframe cover. Don't forget the carpet set as well. The actual steering column and rack can be re-used. You'll also need RHD wiper assembly: it's completely different.
Obviously the original bulkhead has to be cut out: leaving the chassis number undisturbed. Best way is to cut worst of it out, then move outwards until the seams are un-picked. The problem is that the new dash won't go in as I assume the shell starts with the bulkhead, and everything else comes off from it. Therefore the new dash needs letting into the ends of the original. You also have to be aware that you need to unpick around the screen base: you really need to weld supports upto the roof to stop the base moving: otherwise there is a very real risk that the screen aperture will move, leaving the screen tight (risk of breakage), loose (risk of falling out) or distorted (screen won't go in at all).
The offside foot well is wider than the real RHD, so a section has to be removed from this, and the side of the panel moved over, and re-welded. Otherwise there is no room for the accelerator.
The pedal area of the floor needs removing: a this point the whole of the dash, bulkhead, and some of the floor is missing. This is the time to worry!!
Placing the pedals is tricky: I made a template from the RHD floorpan, plus used digital verniers to recheck everything.
Even if you've done everything pretty well, it'll probably still show that it's been done: particularly from the underside.
Overall, even if the car is down to the shell, unless you have done an awful lot of this sort of work (I've done about a lot of restorations, had a restoration business, and done conversions on Triumph TR's before) this is something else. Because the bulkhead is so very different side-to-side, and so deep into the structure of the car, you have to be incredibly careful, organised and well informed. It would be very easy to build a twist through the car.
Your welding has to be 100% reliable: not just because of safety and strength generally, but because so much of it can be seen but you can't get to it to grind/linish welds: therefore if your welding generally needs tidying then don't do it.
As Bootsy says, a conversion is usually worth less than a correct LHD car, and that assumes a good job. If it doesn't go well, the car will be turned into a breaker.
I really would consider enjoying the car as it is: I've got a LHD 914 currently, and am surprised (having always said I'd never have LHD) how quickly you get used to it. One thing with the 911, if you go to shows, particulaly if there's a lot of early 911's there, you will find nearly half will be LHD anyway: certainly you would not be the odd one out

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