need help/ not charging..I think
I can't chastise you for lack of description, but I still don't follow
How "factory" is the rest of the wiring, I'm guessing pretty much?
You using the factory style isolated field alternator, factory 70/ later regulator?
No10 MAY be a little small, although that is what the factory used for accessory/ charging wiring. You have any fans/ pumps/ other big accessories?
Quickest way to check is a voltmeter
Find out first if you have a drop through the harness/ bulkhead. Turn key to "run", engine off.
Hook one probe to your big terminal where the main cable comes up front (closest you can get to battery positive)
Hook the other probe to your ignition feed coming out of the bulkhead. If you still run factory ignition, this would be the "key" side of the ballast resistor, the traditional "dark blue."
You don't want to see more than 1/2 volt, and that's generous
Now see if the regulator/ alternator are getting field power.
Pull loose the regulator plug, ground one probe of the meter, an probe both terminals in the regulator plug. With key in "run" you should see power at BOTH
If this is OK, Start the car, run at an RPM to simulate "low cruise" and check voltage to ground at your "big stud" where the battery cable comes up front. You should show a MINIMUM of 13.5, and you want to see more like 14.
I would usually suggest you inspect/ suspect the bulkhead connector, but you've had that apart "in the build" right?