I have a lead on a 1968 240. How tough is it to convert to left hand drive?

 

you'll need so many parts it's a never-ending effort. Start by getting the Left hand DASH.
and then moving the Emergency Brake to the left, and then the wipers, it's like re-manufacturing the car.

the 420 shows up often in the South and West in left hand drive and with little rust.

here's one for sale in my area, sounds like a lot of TLC has gone into it and it is a USA (LHD) car:

http://www.vc-cars.com/anticcar_details.php?RID=1078

there were 2 others in Miami but sold, one for $45k, one for $7,500, so the price of the above is below the middle.