Welcome to the board!
Your local NAPA will be able to get you a FelPro engine seal kit, along with the other stuff you are looking for.
If you rig already has a points type distributor in it, then I would just upgrade it to the Pertronix conversion kit. Do that will keep you from having to modify the original wiring. I run the Pertronix, and I have no complaints. Plus the conversion was a snap, only took me about 30 to 40 minutes to do everything and be driving with it.
Look up on the Pertronix website for a dealer near you, that way you can just walk up and get the parts. I looked for the Boise area, and there is one dealer close to where my family lives using their zip code.
http://www.pertronix.com/search/dealer/us.aspx
If you are already set up with the HEI, then just rebuilt it with a new cap and rotor from along with new plugs 'n wires from NAPA.
You can also check out the big box mail order houses like Jeg's or Summit.
http://www.jegs.com/
http://www.summitracing.com/
Just a few suggestions...
Not really sure of the direction you are going with your truck (Custom, stock, hotrod).
If you are just wanting to go for convenience to get you daily driver back on the road then NAPA will set you up for sure.
Have fun!