I thought 3L stood for 3 litre which was the F1 engine size introduced at the start of the 1966 season to replace the previous 1.5 litre formula1. The Lotus 25 (the first monocoque chassis F1), introduced in 1962 and 33 in 1964, were the last two 1.5L cars from lotus. Both were highly successful winning multiple GPs and the world championship for Jim Clark. They are very small and slim. The 3L cars were immediately much bigger so make better slot cars. Because the Lotus 43 (BRM H16 motor) was late, Lotus ran a 33 in the early part of the 66 season with a 2L version of the Coventry Climax engine, so it just scrapes in as a 3L. This was hopelessly outgunned, even with Jim Clark driving it and looked ugly with the bigger pannier fuel tanks which were needed in 1966.