Then again, you could do the 64k with crap timing & still call yourself an ultra-runner... hmmm. But seriously, you don't want to be the dude who DNF or did not make the cut-off - that'd be kinda.. well.. embarassing! it's true & you know it! 64k on a terrain like this is as good as any flat >100k ultra.
So dear boy, do me a favour & focus on securing a decent form & decent time & decent result for the 38k, run it strong, run it good. And if you're gonna get competitive & all, you're only allowed to stop to take pics ONLY when the views take your breadth away.. which I suspect will be quite often.. hmm. So no, don't think that's gonna work. Back to just running strong & good then, & fast (for someone ur level)!
1300m in 10km. Good luck buddy. Them legs are gonna hate you!