Anything is possible but I think you’re going to open up a real can of worms by attempting a conversion like this. You better be very mechanically inclined to even consider it.
What are you going to do about attempting to flip the rack and pinion along with all of the little assorted headaches that will come with attempting this?
Other than a right hand drive Subaru I kind of agree with the Ford Ranger truck option. Our local rural mail carrier currently uses a Toyota Tacoma for this purpose and has had the same truck for about 8 years now. His prior delivery truck was a Ford Ranger and he has had no problems with either one; either mechanically or the suitability for the job.
Other carriers around here generally use full size vehicles and the majority have column shifters but there are some who have been at it a long time with floor shifters and don’t have a problem. Several left hand drive Subarus, an old Toyota Tercel, and a few Ford/Chevy full size pickups for instance.