Bellhousing is good. 750DP is good for the 408. Performer intake iffy but ok for now.
As far as the heads go, you go after what your budget allows unless you want to hold off and save up for something "better". If you are patient (while you are working on other sub assemblies) a pair of heads might come up for sale that will fit your build. Something better than what you were going to settle for. It always happens. As for the cam selection, everyone has their opinions/suggestions but it's always good to start with the mnfr's tech folks. Most are very good about working with you on figuring out good cam options. The only drawback is that they will want to know certain info on the motor/drivetrain that you may have not figured out yet. Still (on paper) you can develop an idea of what everything should look like.