How horrible would it be?  This is a prog team, I don't have many options, but I've got extra PA at OF I can shift over to SS.  

I have never tested this stuff, but if I am reading admin's response to JohnGPF's question correctly, here's what I think happens.

Take his existing fielding grade in OF (an A). Figure what the median fielding percentage is for an A shortstop in that season.  If he's a modern guy, figure something like .980.

Take a 2% penalty off of that for playing out of position.  .9604.

Then take 3 consecutive 4% penalties off of that for moving 3 steps the "wrong way" on the defensive spectrum: OF --> 3B --> 2B --> SS.
I get ~.850 fielding percentage.

For his range, figure the median range for an A+ shortstop.  If he's a modern guy, something like 5.75.

Take a 10% penatly off of that for playing out of position: 5.175.

Then take 3 consecutive 15% penalties off of that for moving 3 steps the wrong way.

I get 3.18.

Looks like a D-/D- to me. And a "bad" one at that.

If you try it, let us know how it goes.

Yeah, sounds bad, but my only other options seem to be SS D/D- types with very bad offensive stats.  So I think I'll give this a try, unless I get a decent trade offer or land a usable AAA SS...

Worked for the Tigers in the 1968 World Series. Mickey Stanley. 

Are you trying this with 1964 Willie Mays???  

1930 Johnny Frederick is the OF.