1966 C10 with an electrical gremlin- help

[TxGoats]

Howdy folks, long time member but I’ve been away a few years. I picked up a ‘66 C10 that had been sitting many years. Have it running great with a 350 Crate motor, new bed, suspension, cab seals, body mounts, new seat cover and flooring. It’s mostly rust free except the driver door rocker. I love it, I have also restored the old Clardy Jet Star under dash air but I have an electrical gremlin I can’t figure out. Here are the particulars:
63 amp one wire alternator
New battery, ignition switch, restored wiring from ignition to starter, new ground straps, new cables.
Issues:
Starter will intermittently not start regardless if it’s hot or cold when starting but will always start with a remote starter.
Voltage shows 14 volts at the fuse box when started and alternator excited but when I turn on my headlights it drops to 11.3 volts but the battery doesn’t drop but maybe a tenth of a volt and turning on the ac is worse. I’ve disconnected each fuse and no changes, disconnected the wiring to the back lights, no change.
Any idea where to go from here? Time to just rewire this old guy?
Thanks for any helpful advise.