Sounds like a good plan.
But then, I've never installed greens. My recollection is that they don't require any location at all, so then the center spacer would be redundant. That is to say;not required at all.
The tapered axles, I'm assuming, are the old style, with a splined,bolt-on flange?
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But, if, by tapered,you mean to say that you want to use the tapered timpkin bearings, then they absolutely need locating.Then your plan will work for a little while, assuming you can cut and finish the spacer to establish the correct endplay. But what happens, down the road, as the bearings wear,and the endplay gets excessive, and there are no adjusters?
I suppose you could install a shim pack on one side, and then install/fit your spacer.Then you could adjust the endplay with the shim-pack.
Nuttin' wrong wit dat idea,'cept da hassle of changing shims.