Just a follow up to bring my saga to a conclusion.
The gas utility company tied into the building and I converted all the units from propane back to natural(they were ordered 5 years as nat. gas and were converted to propane at that time in anticipation of nat. gas coming one day).
Everything went well.
Upon startup a few of the hot air furnaces clearly had a "hotter" flame for a second or two but other than that no discernible issues were noted.
It's been about a month now and the first set of gas bills are starting to trickle in,with noticeably lower costs vs.propane.
The tenants are happy!
Thanks again for everyone's help!