14.5 volts is the upper end of "OK"... no immediate danger. If it stays there for many hours, battery life may be shortened.

Are you running the 5.7 with original computer or converted to carb? I believe the computer has sensing and adjustment logic to increase voltage to around 14.5 after a cold start and back off a little as the battery charges and warms. If running the factory setup try to get a service manual for the donor vehicle. There might be a sensor or something that needs hooked up and/or installed or it may be working just as intended. The low voltage excursions may also be the ECU's way of checking the batttery condition.

If you have converted to the 70's "flat pack" regulator, it should back voltage off to 13.x as the engine compartment warms.