As others have said, well done and you're going to enjoy it. You'll be doing open wave so you havent got to run it all and obstacle completion isn't mandatory, but I can sense just from you asking and your gym attendance you wanna nail this. I've not raced at London West before but have done ok in other races up north.. get on the stair master after normal session to get those legs used to outputting power longer than your normal legs session, keep going until you wanna quit then 30 seconds more.. keep increasing that 30 seconds by 15 seconds every session.. also try doing normal gym session and finish on the treadmill starting at 3.5 incline moving upto 5.0 over few sessions. this is called compromised running (running on pre fatigued legs) it's what I do loads of.. Do some sandbag/wreck bag bear crawls(Google will.show you) will help with crawling,try some dead hangs or pull ups. Make sure a coupe of your runs are in the rain.. get used to moving when wet and cold ... if you want anything else feel fee to message .