Warren,
Welcome to the Shopsmith Forum. It sounds like you have been looking here for sometime and have now joined.
You have me puzzled by the statement,
The previous (original!) owner of this piece never offset the motor.
I am not sure what you mean by "offset the motor."
As JPG said pictures would help describe the problem you are having. I have restored 24 Model 10E and 10ER Shopsmith Tools some with and some without the Speed Changer and none required a different motor mount from the original that comes on the Model 10's. It has slots for the motor to mount on and with the slots (90 degrees to the Motor Mount slots) that come on all the brands of motors I have seen on Model 10's there is not a problem aligning the pulleys and belts. Those motors include mostly A. O. Smith 1/2 HP, some A. O. Smith 3/4 HP, GE, PowrKraft (Montgomery Ward) and Craftsman plus a couple other brands. The picture below shows a Speed Changer in place on a Model 10ER with an A. O. Smith Motor. Although the belts look out of line it is the angle of the picture making it look that way.
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- Speed Changer in place.jpg (88.63 KiB) Viewed 1134 times
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The Speed Changer uses as it came from the factory a 22-1/2" and a 25-1/2" belts although 1/2" increment belts are difficult to find. 22" & 25" (4L220 & 4L250) belts work fine. The Pulleys that come with the Model 10's being a 2", 3" & 4" step pulley are correct and the ones that should be used.
I am not sure what extended posts you are finding on eBay when you say.
eBay has some mounts with the extended posts for not terrible costs, but I was wondering if there were any other options.
The only thing you need to do to change the belts around from low to high or vice versa is raising the Motor Mount after loosening the Headstock Set Screws the same as changing the speed without a Speed Changer.
In case you don't have one, a PDF of the Speed Changer Instructions is below.
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