don't do it unless u strait up get a 40t frame. the desirability of the hard tail moby is solely due to its aesthetic appeal and lightweight, by converting a 50v you won't get either and will sacrifice handling performance.
that said 50v's look good even if you don't go rigid. just take off all the shit on them.
51v's aka travelers look even cooler:
note the rear shocks on the yellow traveler on the far right mount at the seat post unlike the 50v's that mount on the rack giving the bike a much more aesthetically appealing stance when stripped down.
But the 40t hard tail really is an attractive moped:
No frame whatsoever where the shock would be just like a modern bike.