Volts really high with acceleration.

AJ/FormS said

the alternator field coil is supposed to be seeing battery voltage at the one brush? ... you can just go out and manually ground that brush on the VR side and drive the alternator into overdrive,right? And you can. This is called full fielding.

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Correct for the later electronic Vreg w/ an alternator w/ 2 field terminals (low-side switching), but not for the OP's 1968. The OP has a mechanical Vreg which uses high-side switching to control the field current, with the other terminal grounded to the case. Today, one can get an electronic Vreg which does the same high-side switching and can bolt in place of the original one.

OP, measure the voltage difference from Vreg case to its "IGN" terminal. If it holds ~14 VDC, then the Vreg is doing its job. Then measure the drop from Vreg case to BATT- and from BATT+ to IGN terminal. Both drops must be <0.1 V for the charging to work correctly. If you measure higher, search for the voltage drop. The case is simple, just run a dedicated ground wire as mentioned, instead of relying on a rusty sheet-metal screw like the factory did. IGN follows a tortuous path thru the firewall connectors twice and the key switch, and is a common cause of voltage loss and thus over-charging.