There were not many of the original #304 sold and I don't have any statistics as to the ratio of the most often seen one with the red roof to the all yellow variety. However, if it is something like 5:1 then that would imply that the all yellow one ought to easily make the 'Top 10 Scarcest' list.
So I was delighted to get the one shown above which is also in excellent condition.
These are the only varieties you'll find of the original model. The 304S is nearly always silver plated with a competition stripe but there is a white version too. That's pretty scarce too.