How to determine a safe red-line?

Run it at a drag strip on a good consistent day and try different shift points. What harmonic balancer is on the 360? stock, aftermarket, internally balanced...

As for the oil pressure being 64ish PSI reved up, is your bypass spring letting unfiltered oil by? The oil is to help cool the internals along with lubricating obviously, but if it's being forced through the system at a higher rate is it able to attempt to cool? Kind of like not running a thermostat for the coolant, if beat on long enough it may overheat.

I like the seat of the pants feel for the shift point or the certain tone of the exhaust at that point, but these responses will vary from person to person.....:)