Answering my own question maybe, but looking at this more it looks like my only option is to have the Stocking U/M be ounces and setup a purchasing U/M as gallons. Really don't want my inventory to be listed in ounces though. I guess the answer I need is if this is correct or is there something I am missing? Thanks!

You might look at an add on called the Formulary.  

Also, just add the product to your inventory as ounces, not gallons.

Original thought was to just stock in ounces but I have existing products that have been using gallons for several years. Won't that wreak havoc on previous periods inventory/COGS reports if I change the stocking U/M? Wouldn't I have to deactivate existing products and start over with new products? BTW I have this same issue for items we purchase by the ton and use in assemblies as pounds. Thanks!

How many items do you have?  You could create new id's as you order new merchandise in and make the previous numbers inactive.

Changing the U/M is not going to affect your previous period inventory/COGS reports.  You'll need to adjust your current inventory levels to ZERO and then adjust back in at the appropriate unit cost for OZ.  Example: adjust out qty of 1 GAL at $64 ea and adjust in 64 OZ at $1 ea.  If you have assembly BOM's you'll also need to change those qty requirements to be based on OZ.

Ok, can probably verify this in documentation somewhere, but if I set my product up with a Stocking U/M of OUNCES and then a purchasing Multi-pack as GALLONS, no Sales Multi-pack; the U/M for the BOM will be the same as stocking U/M of OUNCES, correct?

Have a similar issue with TONS/POUNDS except there I will need to set product as POUNDS in stocking U/M, Purchasing Multi-Pack in TONS and then Sales Multi-Pack in TONS. With that setup, which U/M will the Assembly BOM expect? We sell it as TONS alone but would like to use POUNDS in the BOM for other products.

Thanks!!!

Yes - BOM U/M = stocking U/M ... pounds on the BOM.

I did not recommend changing the units like that because if you do look back you will not know which calculation was used.    Just a thought.    

So can I change the ID of the current items and then create new ones using the old Item ID? The item IDs match to other production software and would like to keep the same IDs in both places if possible.

Assume I would adjust inventory to zero on changed IDs and set beggining balance or adjust inventory on new items?

Thanks for the help!

Yes, you could use Change ID and change the items, but that would change the ID's throughout the program.   The ID # would not remain the same in assemblies.

How many items do you have?  Can this be done in a day or do you need a week?

You could invoice the old items out, and invoice the new items in.    That would wash the items.  There are several ways to do this.  None are wrong and none are right.  It will be your way!!