which heads for a 408ci?

Find out what the matched springs are for the Comp cam and if they'll be a problem swapping them on to a set of the Edel. heads which I wouldn't use for this type of build and then cross ref. them with some that would fit better on the head.

Nothing wrong with porting heads, the heads you have, but to purchase Edelbrock heads and then port them isn't what I would call the best move. Being that your not paying for the porting, per-say since your in school for this type of thing, I'd call it a learning exper. on porting a head. But still not the best move.

The Edel. head can do a 500 HP engine without porting if all else is in line.
The Edelbrock web site used to have and may still do have the section on Mag. stories were a 360 (@ .070 overbore) pulled 500+ hp with a Comp Hyd. 308 cam. I'd read the story first.