I think it might be easier to find complete doors from a earlier model. Just my 2 cents worth.
But you still don't get the push button handles.
I think the conversion kits use plain 4 or 5mm thick glass and not the metal framed glass you get on the pre-51 doors.
I'm sure you could use pre 51 framed glass but you would need to buy separate window channel and door inners,to allow for the extra thickness.
It might be more hassle than it's worth though.(JMO)