John - I think IMHO cosmetically all the reproduction Tachometers (CHQ & OER) are very good facsimiles of the original AC/Delco. I have several 69's and the colors are good matches, the finishes are best possible. The obvious difference is the embossing of the rear shell with the CRG or OER brand-mark. AC/Delcos were unmarked on the rear, often just rubber stamped with a date code.
Mechanically I have not seen any difference on my 69 with vs. the AC version. I know some folks claim they HEI worked driving a reproduction tachometer with no conversion or filter, but I have no experience with that.
