Well, my G&E shaper dates to the late 1920's, or early 1930's
We discussed this some time back on this forum
http://www.practicalmachinist.com/vb/antique-machinery-history/g-e-shaper-205543/
The SN is a lot smaller than yours, 667A8, but of similar format.
My G&E was made in NJ, not MI.
At some point Mitts and Merrill bought G&E, but long after my machine left the factory.
Condition and features are more important than age when assessing a shaper.
Hold out for one with a vise that fits correctly. The G&E vise has a tapered hex and mating wrench/handle, so get that as well.
Automatic lubrication system - mine has one, but smaller G&E's of similar vintage are seen without them. Unless you plan to run the machine with an oil can in both hands, get one with an oiler.
Power down feeds are nice, but not that common
Universal table - versatile, but they have to be set and reset. Some love them, some hate them. I would sacrifice the rigidity for the versatility on my machine.
Condition - Almost all shapers are old and used hard.
Inspect the head carefully for signs of repairs. They can be crashed into the column and break out in the dove tails.
Open the side cover and see how much play the crank arm and slider have. Verify they are not brazed up.
Verify the power feeds work in both directions.
Run it with the bull gear in high and back gear. Listen for periodic ticks indicating damaged teeth.
You can also roll it over by hand and see if you feel anything.
Parts - assume they are unobtainable and plan to make your own.
Your in the ball park on price and weight. Scrap value or slightly less is a good opening point, but you may have to move up to buy a good machine.
Dating the machine -
Patent numbers on the machines data plate will give you a "no older than" point of reference. Just pull up the US patent office web page and put them in.
I have noticed a few other shaper features that seem to date them.
No clutch lever - OLD over head flat belt design or new hydraulic shaper.
No oil pump - earlier design than mine
Open power feed linkage - early design, like mine.
Enclosed shaft type power feed system - later design than my machine.
Motor integral to machine, not hinged on back - newer design than mine.
Base casting does not extent past front of knee/ support foot inside knee - earlier shaper designs.