You don't have to adjust the valves running or hot. People have been making those adjustments since the beginning of the internal combustion engine cold.
The slant is the first engine I've come across where the manufacturer recommended a hot adjustment. Granted most of my valve adjustment experience is with European stuff, but even the old Fords I've messed with gave a cold spec only.
Plus, how are you going to get a brand new engine hot to set the valves the first time? Aim a blowtorch at it?
