I would tune it to 465 MHZ, which means cutting it to the following lengths.
L1 needs to be trimmed to 15 3/8 inches
L2 needs to be trimmed to 9 13/16 inches
However, do not try and trim down to the specified length at once. (Trust me I know, I screwed this up once), Cut a little bit off at a time toward the desired length. After cutting L1 and L2 a little bit each time, re-attach them and measure the SWR again, and then cut again, etc. You will slowly see the SWR starting to come down. The reason for doing this is to not accidentally cut it too short, in which case there is nothing you can do.
Side Note: You can get a really good SWR, DO NOT try to get a perfect 1 SWR. Is it possible? Yes. Is it easy? No. Most people consider any SWR lower than 2 as a " good" SWR. Me personally, I try to get it close to 1.5.
Also having said this, do not do it immediately! Some one else in this forum may have a better way than I know of. There is a wealth of knowledge here!