Time to plan...
And no, stock heads won't do a 408 with a BIG cam justice. You could put $1k into them (porting & polishing, valves, etc) to make them work....
And don't take this wrong, but what you're talking about doing takes a lot of knowledge. I know a fair amount about cars and I needed help. Things like degreeing a cam, setting the valve train up properly, installing a clutch that will hold up to this much power, tuning.....you're gonna need help, so plan for that part of the budget too.
And on a serious note, good luck with whatever decision you make Josh.

