My Brother in law has a very old furnace which still works in their home. They believe it's nearly 45-48 years old. The only info on the plate is: Superior Furnace Mfg. Co, Plymouth, Mich. and the numbers 611788. If there's any possible way you can date the furnace by this info, would appreciate it. A local furnace dealer is offering to replace the "oldest furnace" in their area. Any help is appreciated.