The oil tank is in the main down tube from the steering stem.
Not sure if the 500 was a head cracker too. It's a lot bigger head so may be longer lived. Ballards in Penrith used to weld the cracked heads up and also welded the big fins onto the big fin heads on the next family of motors after the RFVC ones ended. That's when they were XR'S Only. They turned my old 89 XR250 into a big fin head and I got it bored out to 280. Wish I still had that bike now.