Help me identify this Ford engine for a customer...

The stock piston choices can be a real mixed bag too! Stock pistons will have what a person would think is the cubic inch of the engine cast on the piston pin boss area, but no, variations were common. A 390 could have a piston with "360" on it which would make it a higher compression version 390. OR a 390 cold have "410" on it which would make it a low compression 390. Many a person had their hopes dashed when they found out that NO its NOT a 410 (same crank as a 428), it's just a low comp 390.