That doesn't look like the back of a 2004 and up Custom riser. Not trying to argue, but it looks like it may be the the riser off a Custom that's 2003 or older (straight risers instead of the curved '04^). That's why I was curious about the depth of the spacer.
The back of my 2005 883 riser has a relief cut to allow for the fork-stem nut. Also, the back of a 2004^ Custom is more continuous across the back, due to a plate (which has the relief cut) that attaches to the main riser component. If you flipped a 2004^ riser around, your speedo woud be facing the wrong way. If you have a 2004 or newer Custom, I'm sure you've thought of all this. It just makes me wonder what we're looking at in the pic above, and how does it differ from an '04 and newer.
The back of my 2005 883C, that's been powdered gloss black:

 

I'd like to bring the bars on my '06 Custom up/back a little, like to the limit of the existing cables, perhaps.

 

Hmmm, I was talking to the guy about it and he showed me pictures and said he had a factory custom riser that he flipped around then rotated his speedo to face the right direction. Maybe he has a 03 or earlier model. Thanks for pointing that out. I thought I covered all my bases and asked the guy 100 questions. He is a member on xl forum and on facebook. I'll have to ask him again about it. I did order the part already and it was only 25 bucks, so when it gets here I will see if it has the same shape of the bottom of the 04+ custom riser.