Call VP, their tech assist people have always steered me right. Need to match up octane need and burn rate for that size cubes cr and rpm. IE a pro stock engine needs a fast burn rate because over 10k rpm. They will tell you what’s right for your set up. C25 would be my guess for N/A max effort. But not sure if those heads and your Rpm want a fast burn fuel.
Is it just a big reliable bracket motor or do you want to leave your mark with a max effort build. I don't know much about bracket engines with that high of compression but I certainly know what to do for Max Effort. That is send it to Bob Book for dyno break in, a carb and dyno tune up of whatever fuel makes the most power. You will never believe the carb he picked for my 399.
The dyno break in is really cheap horsepower that will last the life of the engine. Proper ring break in is of utmost importance. For me it was Q-16 every time. I not only made the most power but has the biggest tuning window for mix, weather, timing. C25 was substantially less power but also has a very narrow tuning window.
It's nice to be the hunter. I personally come up on guys with a 30-40 mph advantage. Gives me a lot of options to know if I have won long before the finish line. I often pass people at the 60' mark so I know they are late so it's easy to keep them covered while throwing candy and shirts to the crowd.