Under the hood are two main harnesses. One is the forward lamp harness the other is the engine harness.
The forward lamp harness for the gauge dash has two additional wires that are for the AMP gauge. You can use your existing forward lamp harness temporarily; you will not have use of the AMP gauge until you get the new harness.
The engine harness is the same for sweep or gauge dash. It is also the harness that is typically in the worst condition. It's a good idea to replace this harness as well.
You can contact M&H
. It's my understanding that you can have the two new harnesses modified, forward lamp for the one wire alternator and engine for the HEI ignition.
The gauge dash harness should have a brown wire, for the tach, that gets a new hole through the firewall. You will need to change the connector for the HEI dist.