Stop in for a cup of coffee

Trying to figure out the actual fan center to get shroud centered . this is exactly where the fan is centered on rad. 17 inch fan with 1 inch gap

View attachment 1715783565
I woulda installed rad,took pencil and traced around on cardboard with fan blade as i turned it. Add 1” to diameter Measure between rad and 1/2 way into pitch of fan. Build box out of steel.