It could be a loose connection, bad battery, bad generator, or bad regulator (alternator took th place of the generator and regulator in modern cars). Once again the shop manual is a good source for diagnosing problems with the electrical system. I bought a shop manual from Ecklers, but they are available from any of the old Chevy truck part suppliers. Personally, I've used Jim Carter and Classic Parts of America (Chevy Duty). You're probably going to need the manual to help with most of the repairs and maintenance, anyway.
As far as "upgrades" to the electrical system, I recommend a Pertronix conversion kit. It will keep the stock look-much neater, more natural appearance IMO-while providing the reliability and reduced maintenance of an HEI ignition system (modern ignition). If most of the wiring looks bad, you might want to consider buying all new wiring as a kit. I'm doing it the slow way by replacing wires individually, but I'm also not replacing all the wiring.
To a certain extent, I agree with Red58. Changing the ignition system at this time would be a mistake as it just adds one more potential problem (if done wrong). However, if you can get it running, I think the Pertronix kit is a very slick upgrade from points (though I did keep my points just in case

).