To convert the F104 to a wide car, all you need is the front arms and kingpins, total cost is about £10. The carbon reinforced arm, part number is 54153, is stronger but the standard arm, part number 50503, will do the same job. The carbon reinforcement doesn't make any difference to handling, just makes it able to take more impacts without breaking. You then need shorter kingpins, part number 50508 to fit inside the smaller wheels. Steering arms and springs are the same on both cars.
You then just need a set of Tamiya F103 or 3Racing F109 wheels, or any tyre made for the F103. I would recommend a set of
F109 tyres as they work great on carpet and easily the most popular tyre in the UK.