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I have decided to install a small step-up converter to run the 12v lights on two supplemental gauges I am currently using, as well as the monitor for a 12v backup camera I am adding (I'm not ready to take on a 12v conversional at this time). The wiring diagram is pretty simple, ie neg and pos leads to the battery and neg and pos leads to the 12v load. No special steps are given concerning the change from positive ground negative ground. Is that change addressed internally in the converter or is there something I need to do to account for that change in grounding during installation? As always, thanks for any and all comments.

Your Packard is probably positive ground (unless someone changed it on purpose or by mistake) so be sure that anything that gets mounted doesn't have a negative grounded housing of you'll have a short.

Gave no info on what device you're using so I'd contact the manufacturer before confirming anything.
Not the first time this has been done.

It's common to run different voltages in the same cabinet, with proper shielding, so I don't see any issue so long as you run a separate ground wire for the 12V devices* and isolate them through the mounting hardware from the car ground. Watch the routing so no signal distortion. May need some plastic hardware; washers and fasteners, etc.
*- There's no circuit interference, if you're not connected to the 6V circuits. You can power with the normal +- protocol, the car won't know any different. Very little power draw here.
The digital camera is probably running on some voltage other than 12V and just powering a transformer with it. I have one in my boat engine cowling that transmits to the truck so I can see behind. It's powered off boat 12V but runs off a transformer and has a WIFI transmitter.

Yup on the car being positive ground.

Fish'n Jim - I can provide specs or brand/model for the inverter and/or the same for the camera/monitor if that's what you're asking about.

Here's what I have so far. I mounted the inverter to a metal panel on the inner fender of the engine compartment (steel screws through a steel panel), so I imagine the inverter housing is grounded to the chassis. The black and red wires on the input power supply side of the inverter are connected to the appropriate battery terminals. A yellow wire on the output load side of the inverter is connected to the supply terminal of a switch. The switch is mounted to the metal dashboard - but is in a plastic housing - so probably not grounded there. I have a bus bar for connecting lights in gauges, the monitor for the backup camera, etc. The bus bar is powered by a (yellow) wire coming from the load terminal on the switch - making it the red/positive side of the bus bar (true or false?). The earth terminal on the switch is connected to a black wire coming from the other side of the bus bar - making that other side of the bus bar the black/negative side (true or false?). A black wire on the output load side of the inverter is connected directly to the black side of the bus bar. The bus bars are mounted to a wooden panel with metal screws but those screws do not come in contact with any other metal, so no grounding there. And then there's the ground from the positive terminal of the battery to the engine block.

It took me awhile to write that out, but the process gave me - and hopefully you - a clearer picture of what I have. So the big question is, does that setup give me the proper grounding to safely run 12v neg ground devices from the bus bar or are changes in the grounding called for?

PS, I connected one of the gauge lights to the bus bar for a test and flipped the switch. The gauge light went on, as did the light built into the switch. I am not taking for granted that that means the system is properly wired as I believe those little light bulbs are more forgiving than more sensitive electronic devices will be.

Looking forward to your response.

PS Below is the layout. The art skills leave a lot to be desired.

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Got it! I finally understood what several of you were trying to tell me about not using the same ground, ie not grounding both circuits to the chassis. I also had a friend work his magic with his ohm meter before I lit it up. Every thing works with no FOOM! Thanks for the help.

I have used these gizmos in my 38 to power a radio and a backup camera (just to make sure I used a separate unit for each.) You can ground your radio,camera etc directly to your chassis ground. simple 3 wire hookup.ebay.com/itm/NEW-6-8-12-Volt-Positive-to ... h=item5486084b6e:g:6QUAAOSwl9BWKXZF