I think there's been a little misunderstanding. . . . you mean you priced out the components of cap, rotor, coil, coil cover, and module you figured it was cheaper just to buy a whole complete distributor? I don't think you need to replace all of it. I don't think it's the failure of the pickup coil either, but maybe . . . .
there's a ton of info here:
http://garage.grumpysperformance.com/index.php?threads/trouble-shooting-rebuilding-hei-ignitions.2798/I'd start by checking the resistance of the pickup coil. The connector is to your right of the module as you are looking at it in the truck. Should be two wires going into the connector. When disconnected from the module, the module will have one smaller blade and a larger blade. Be careful pulling the connector because inside those wires like to move. Using an ohm meter check the resistance between the two wires. See if the reading stays when you wiggle the wires to make sure there is no break. Should be about 500 to 1500 ohms. There should be NO continuity between either wire and the distributor body. Make sure when reconnecting the module to the pickup coil connector that it makes a GOOD connection. I've been bitten by this a few times when I got no spark. Also verify that there's at least a little of the heat sink compound between the module and distributor. Not a lot, but some.
The cap and rotor can be checked visually for the most part. You're looking for any melted pieces or burned through marks. Along with making sure there's a ground strap as mentioned earlier, is to verify that you have the button in there correctly. From bottom to top, it's cap, button, rubber gasket and then coil. You can also check the resistance of the button at this time too. Should be 5k ohms or less. If the ground strap isn't there, there should be a new one in the package if you buy a new coil.
I think you can get by with a stock style coil and module. You could either hit the boneyard for a cap cover if you need one or get it from rock auto. I wouldn't necessarily get AC Delco, since they don't make anything anyway. Like I said, stock STYLE.
MSD makes some decent distributors that are for use with a box only but I believe you can also wire in a 4 pin HEI module to run them as well as a potential back up. But I think that's pretty overkill for your application. A decent stock system with .045 gapped plugs and some timing mods should put you right where you want to be. I'd still say external coil, but that mod is a little more involved than you may want to commit to.
Profom makes decent distributors, they make the GM ones I think for some of the crate motors.