radiators can only be fit to a car with watercooling system so there is absolutely NO truth in what you have heard. also almost all VW beetle engines are essentially the same and they can all handle upgrades like external oil coolers etc.
under the skin almost all beetles are the same (except autos, post 68 US models and the supers)
autos, post 68 US spec cars and supes have Independant rear suspension and handle a little better. the 1302 is the epitome of the VW beetle, the 1303 is the same car but with slightly changed suspension (up front) and a curved windscreen which was made to cope with US crash safety issues.
BTW the "bari light wali" is pre 67 (sloped headlights), unless you mean the one with the big tail lights, in that case that woudl mean the 1303 from 73 or all beetles from 74. the 1302 has a "tombstone" tail light.