Learn to solder correctly and buy some appropriate size heat shrink. Much better than butt connectors and with marine grade heat shrink it is impossible for it fail and easily hidden in loom. I solder virtually everything in engine harnesses other than 12 volt feeds.
The pink wire that feeds almost every GM HEI should be a 10 or 12 gauge wire that needs to carry about 30 amps. A properly sized butt connector will be more than adequate, but soldering is better. After the initial lay out of $35-40 for a soldering gun, some small gauge wire and flux, and some heat shrink, it works out to be cheaper than quality butt connectors. I buy heat shrink from Fastenal in 3/16" and 1/4" 10 packs.