His PR is 3:59, so to expect anything better than 3:40 would be a stretch.
Brazier has freakishly good natural endurance. At the state meet in HS, he lost to Grant Fisher by 40 seconds and finished 6th in a tough state all while having never run more than like 6 miles in his life and not wanting to run xc.
He’s run 3:59 in 1 attempt with a 54 close as rust buster. He’s probably a lot closer to a 3:33 type dude than you think. For this race, I’d say 3:36.