Data Tech and Weston digital Panel Meter info from the mid 1970's

[trobbins]

I'm progressing through the restoration of an RFL Industries AC/DC Calibration Standard model 829G from the mid 1970's.  Unfortunately this unit is missing its Digital Panel Meter. 
Luckily the 829G manual was on-line here: https://www.davmar.org/pdf/RFL829G.pdf, and an advert is shown here: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5213241.  But the manual is a little short on details.

This equipment either used a Data Tech 344-2, a Data Tech 4212-02, or the Weston Model 2471 DPM.  I can't really locate any relevant catalogs or adverts for Data Tech or Weston's ranges of DPM's, or a manual for those specific models.  The attached photo of a Data Tech below would be similar, as it uses two separate rear connectors, with one connector related to options.  The optional functionality in my missing 4212-02 model appears to include an over-voltage/range signal to then trip the unit; a HOLD signal to retain the displayed value; what appears to be a parallel printer port; decimal point inputs; and a front panel full scale adjustment.

From the fault-finding notes, the 4.5 digit meter appears to have a high input impedance and 1.4V max input, which relates directly to an optional Standard Cell used for self-calibration of the equipment's ranges.  The 829G manual only makes passing reference to a separately provided DPM manual.

If anyone has any manuals etc on these DPM's I'd appreciate a post/PM. 

The restoration doesn't pedantically need the panel meter, as a modern meter and some simple form of decimal range display, and perhaps an over-voltage detector, should be fine, but always worth chasing up details if they still exist.  This calibrator seems to have been mainly sold into the defence force establishments, so perhaps uncommon to see in a cal lab.