yes, there is a route. I don't think it is all FSR, I think a short bit of it is just resource road. My last trip thru there was 20 plus years ago in a YJ, I never carried extra fuel. I don't think the distances between gas stops are ever 100 miles. Gold Bridge, Lillooet, I think Gang Ranch sold gas too.... altho COVID might have closed Gang Ranch. I was planning on doing it after the Overland Rally in Whistler last summer.... but that got cancelled. The Caribou is Gods country, I love the high elevations. The canyon and bridge over the Chilcotin River is spectacular at sunset. Definitely spend some time around there.
Or since this is 4 months later, how was the trip....
Apologies for my attitude, old truck driver, when I see 16 hours of driving I think 16 hours of hammer down, 1000 miles.