If one is handy, it is pretty straightforward to make your own translucent numbers plate, an option on many British high end vehicles, including the SVW series. That includes forming the plastic digits, as originals are usually old, different shades of plastic, and brittle. In a nutshell, you need a number plate basic unit, either an original or a new one from SVW spares , if still available.
K939Rear number plate box (complete)SA VA WAPOA Enquire Purchase the ACE aluminum digits that you need from online, they are readily available.
Use these digits eventually for the front number plate, but for now, use them as vacuum forms to make new digits for the rear. This can be done easily with a small dental vacuum machine, say a 6" x 6" unit. They cost around $100 USD and are useful for many other projects as well. Here is a link:
What to use for translucent plastic digit material? Used clean Milk or water plastic cartons. Cut them up into 6" squares. Place your aluminium digit on the base, block with tape the holes that are not near the base of the digit, mount the plastic in the upper frame, turn on the heat, wait for the plastic to droop or sag, then activate the vacuum and bring the frame quickly down over the digit.
The vacuum will suck the plastic around the aluminium digit. Let it cool. Trim, space each digit, and mount, in the proper sequence, to a piece of 1/16" thick clear Lexan the size of your number plate. This eliminates all the water issues as everything is plastic. Use black plastic with PSA one side to frame each digit as per original, but using black thin plastic instead of metal framing. Again, mount all pieces on the clear Lexan panel which fits behind the numbers cover plate. Mount the LEDs behind the digits. Voila! A translucent number plate. Here is one I made for SA2333 Tickford around ten years ago when LEDs were 'unknown', I wired in 75 LEDs A source for the LEDs that I used These are self mounting with 3M sticky tape, I wonder where the black and red wires go
With respect to number plate boxes and digits for the optional 'translucent' version
It is possible to make the digits, but likely only in a full set so everything matches. A set would consist of 4-6 digits. I would mount them to the 1/16" thick clear Lexan, with the appropriate blackouts surrounding each one. Each Lexan unit would have the proper waterproofing foam strips (zero torque foam) installed around the borders for waterproofing. Your job would be to install this unit into the number plate box, and wire in the appropriate LEDs, not hard, but time consuming.
Cost would be $150 per set, including glass bead blasting of the original aluminum digits and your front number plate if you send me the originals. If you send the complete original number plate box I will glass bead blast it, and make sure the Lexan and digits fit for an additional $50. Your job is to make the number box look like new with proper paint etc and add the LEDs. Postage would be extra, estimated , from the USA to say GB, around $75 USD.