Hi Rafi,
Welcome on the forum.
I built a LHD chassis too, as I live in Sweden. And yes, at least for the "book" chassis (Ford Sierra based), I just built a "mirror" image of it. I don't know why with the MX-5 amendments is would be any different., so I think this is the way to do it.
There are "official" book amendment instructions for LHD on the "book amendments and extra guides" section of this forum. Check the other ones too, they are quite useful.
http://www.haynes.co.uk/forums/showthread.php?t=2430
IIRC, the only things to swap are the steering wheel support, U7 and U8 (otherwise you won't have a lot of room for your feet and a pedal box), and the front part of the transmission tunnel which matches with U7 and U8 position.
We are a few guys building a LHD, check the location of the members, anyone who is not in the UK or in Australia drives on the "right" side of the road. There are a couple of guys building the Roadster in the US too you might get in touch with. One of them is StruveD, and he is doing a very fine build in my opinion. You are not really neighbours though, it is a big country
Do not hesitate to ask questions on the forum, it is full of very nice, competent (not talking about me!) and helpful people who will be happy to help. I wouldn't have done half of what I did on the car without the help of the forum members. And please, post pictures as soon as you've started!
Good luck
