Any info about this model would be much appreciated.

You may be missing a few numbers. Are you sure that's all the numbers?

This is what is on the panel by the pilot and lighting directions. My home was built sometime in the early 1970's and we know virtually nothing about this, the original furnace. However, that is the complete model number as listed on the furnace.

Day & Night
Model #: 100U-19C
Gas: Natural
Input: 100,000 BTU
Serial #: BCGGG 39495
Series: 102
Bonnet Capacity: 80,000

Thanks for your help.