Those 781's will work. But they will need bigger valves an some work done to the ports. Here is a good web site with flow numbers. You could probably get a good set of aluminum heads that flow around 280-290 for a little more than the 40 year old castings that you are going to sink a hunk of money. (This my last edit) Stay with oval ports.
http://users.erols.com/srweiss/table...hevy_Big_Block
The camshaft needs to be on top of the game for something like this for sure. You really need to wait until the heads are done so you can give who ever the flow numbers an your other info about your truck. The camshaft needs to be designed around your truck parts list. You need to decide what the Compression ratio, converter, rear gears, headers, head flow numbers, intake an headers are going to be before calling whomever. If you go solid roller that is a whole new topic. We will save that if discussion for if you go that route.
I used
http://www.straubtechnologies.com/ he is not cheap. Last time I ordered from him he used Bullet cams.
If you have not figured out by now. The tranny will have to be a good one. The 400 turbo will work, I would not use a 350 turbo behind this engine if you go the direction you are headed with the engine. A set of 3.73's would be nice too.