I think it's more fundamental than that - there'll be panels in the bulkhead which get punched out at the pressings stage for steering column, pedals etc. Plus different attachment points for the front axle. Once a car is built as LHD, it would have to be individually converted to RHD (or vice versa) with a big dismantling task. It's feasible for one-off specialist conversions or rebuilding classic cars, but for a big batch would not be economic within factory budgets. Much easier to divert them to another market which drives on the same side, even if you have to dump them at discount prices - there were lots of Europe markets taking Imps at the time who could have filled in.