As I am sure you know,
the 400F motor is a direct drop in swap. same mounting points, and everything.
What I don't know is if the 400 is just a 350F overbored, or if you could bore a 400F motor out a bit more to make it *close* to 500?
dunno 
The 400 engine is basically a 350 punched out to 400ccs, new head, new clutch and six-speed box.
You can punch out a 400 engine to take 500 pistons, giving you 500ccs, but it's very labor-intensive and requires some engineering. The result is reportedly worth it.