Adjusting voltage regulator

[russcc]

I have a NORS Echlin 6V voltage regulator on the '40. See photo. The electrical system did not seem to be charging so I took the generator and regulator to a local automotive electrical shop. They ran generator on the test machine, it was putting out about 35 amps. They hooked up the voltage regulator to the generator, a 6V battery, and a voltmeter and ran the generator. The most voltage we could get out of the regulator was 6.3- to 6.4 volts, when we needed around 7.5 volts. They tried adjusting the voltage relay but could not gain any additional voltage. Any suggestions from the electrical gurus on what else to try. I hate to ditch a good old NORS regulator for a new one of questionable quality made who knows where. Thank you Fordbarners.