I have got this regulator that is different from the other 914 regulators that I have.
On the rear side of the regulator, facing the firewall, there is an extra hole machined. Was there any differences with the years, or has this one been modified?

Do you think I can just put in a plug and it would operate the same as another regulator

Does anyone know what this is from, and if I could still use it on my 914 by just plugging the extra hole.

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make sure it is a good proportioning valve to begin with!!

Yep, there is an early up to mid -74 and late mid-74 thru 76