[TRE Cup]

the lamp holder assembly is standard usa spec housings as found on any 65-67 911 and 912. The R used a lot of cibie lamps , due to a sponsor deal with the factory. There are several manufacturers of the concept known as bi-iodine (2 halogen bulbs per lamp, not a kinky sex practice!) From this era, Hella came up with the now super expensive H-1.
But i digress; the correct cibie lamp has a small flashlite sized reflector for high beam and low beam bulb situated behind it. It was not very good, but sure looks cool
Marchal made the amplilux and Carello made a lamp too (strangely very close in reflector design to the H-1 Hella)
These three units will give off a dark grey cast on the low beam side of the reflector, with the bright lower section for high beam. This being during the day.

So... what you need to convert your recently aquired swb is a pair of PORSCHE 911 or 912 headlamp units from 65-67. The 356 and bug units have the same sized lenses BUT attach with a tab , rather than a screw hole through the bottom of the rim.
I suppose if this was a total budget deal, one could kludge a pair of the brazilian VW lamp units (remove the tabs, and make a small reinforcement for the hole required). VW/ 356 units will have a very rounded rim, compared to the flatter Porsche rim
Glass or plastic lenses are available (with plastic in yellow or grey smoke)

fwiw- the cibie, marchal, and carello units are bringing big $$ with ferrari, maserati, alpine, porsche collectors worldwide

hope this helps clear it up