Take a look at these items that are sold by Summit (and other vendors).
Painless Wiring 80112 - Painless Performance Junction Blocks - Overview - SummitRacing.com
Goodmark 4143-374-672 - Goodmark Electrical Junction Blocks - Overview - SummitRacing.com
There is also a stock heavy duty GM terminal strip that is used on late 80's and early 90's GM pickup trucks. It has five posts on it, and it is usually mounted on the firewall above the passenger side valve cover. You can get one a the junkyard for a few dollars.
The older (73-87) GM trucks also have a two-post terminal connector mounted on the firewall near the brake booster. A single power feed runs from the solenoid/starter up to that junction and then it is used to power the fuse box and under hood accessories.