I'm trying to identify the tranplanted V8 in my 57 pickup. The # stamped on the front block tab are F409F and off to the side a 1 space 6. If I also need the block casting number where do I find it ? Thanks for the help.

The block casting number and casting date are located behind the heads in front of the firewall. They can be a bear to read but a mirror will help. The road draft tube is in the way but with luck you can see the numbers.

That would be behind the right head.
The F is built in Flint. The 4 os April and 9 is the day. In 1957 the F was a 283 passenger car engine. In 1958 it was a 348 engine.
If its a 1958 or later it will have the boss and mount bracket holes on each side. A 1957 will not have this.