As far as LH and RH sending units the only difference I see are which way the float sits (either towards the front of the truck or the rear). The one I pulled out which was a passenger side tank sits towards the front..
Assuming nothing hits the float does it matter?
There's probably a reason to face the float forward. It costs more to have two parts where just one will work...
Possibly it'll be more jittery from slosh with the float pointing back... ?
Don't know.
From orbit on my Android.