The old pre 1970 single field mechanical regulators? They worked fine usually and were adjustable. I have one of those mp blue 13.5 volt substitutes, and haven't tried it. Most parts stores also have an electronic replacement in stock too, for the old points style reg. (69 and older)
Parts houses have a wells vr706 if I am remembering the # correctly that is an electronic replacement for 69 back cars but is not identical to OE appearance and someone here sells (or used to have) new black ones that looked OE but is electronic on the inside for $25 to your doorstep (mrrandy was his handle or something close to that so if you see it that's the one) I'd check the parts for sale sections here if that is what you are after.
The new replacements are the best thing since sliced bread.Have them on 3 cars.My kids 62 street driven has been on at least 10 years.Dump the old points one and get the direct replacement electronic one.I changed my 65 to a dual field years ago.If the new style had been avaliable Id have one of those on it.Best part is they just go right in with no changes.Rocky