with resto comes new paint Im sure on all your parts, including radiator support, fenders, inner fenders etc. Grounds are almost always the culprit. Did you use star washers on ground locations such as near the regulator and headlights? The regulator also needs to have its bolts thru the paint for ground as it doesnt have seperate wire ground like the 67 and 68 do. Also have you gone to the Wells modern regulator # vr715? It has electronic guts but exterior looks like original ac/delco. A fussy regulator could also affect the lights with dimming as you describe. Id replace the regulator AND use some star washers on wires that are supposed to ground. Are your grounds in place from frame to body below the exhaust maniforls and off the valve covers? That can help too.