A woodworking forum for woodworking hobbyist and woodworking projects related and unrelated to the Shopsmith MARK V
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(same age as me 
)viewtopic.php?f=7&t=23647[url] Below i ... XBhMHJJY1EThe best place to start is the second post in this thread by Everett Davis. The link in that post is to his google drive which has a restored PDF version of a Model 10ER Manual. It is in the 10E & 10ER Magna file and is the second item on the second row currently. That is the manual that would have come with your Model 10ER S/N R66?11 originally or very close to it. That will help you get started. There is also a lot of other information about the Model 10's in that file group.
You listed your serial number as R66?11. Is the ? in the serial number covered and currently unreadable? Will it become readable with some cleaning of the Logo/Serial Number Plate? Just curious.
The most common motor found on the Model 10E and 10ER tools was the A. O. Smith 1/2 HP Motor which was an option when purchasing a Model 10 in the late 1940's and early 1950's which many buyers did. Of course other motors will work and another common one was the 3/4 HP Motor sold as an option. My last Model 10E restoration has a 1 HP Motor that came with it that was a newer motor someone had replaced the original motor with. Many parts and even motors come available at the online auctions but the motors are quite expensive to ship due to their weight. Finding a motor locally is a better option. Your post doesn't list where you are located but there has been an A. O. Smith 1/2 HP Motor for sale near me recently from a parted out Model 10.
If you want to learn more about the Shopsmith Model 10's I recommend the thread at the link below titled Shopsmith Model 10's What When and Where that I authored.