360 Rebuild for 1974 Swinger

The 405 piston will get you in the low 8s for compression if running a regular style head , that cam will be fine with timing much like everyone else here recommends, headers and moderate exhaust , jet your carb two below stock size as a baseline it will be just fine , you can fine tune it from there and enjoy working together with your son on your project.
You will have a solid baseline and can add to your build as time, funds or need for more happens.
I like the post about cam selection above , awesome.