I used a 10 inch heat shield with my HD turnout.
There is a 7 inch x 1 3/4 inch adaptor underneath it.
The Samson heat shield is a H129 10" x 2 1/4"
Very nice chrome.
http://www.samsonusa.com (click on Accessories, then Heat Shields) I ordered
mine from a local chopper shop, $39.95 + tax
They have all sizes, other companies make shields too.
As for the white spacer, you may have to adjust the Main jet size, since that needle that the white spacer is on is directly coupled to the main jet.
check this chart for different jets used in this carb
Later models are leaner and have more backfiring problems, exhaust leaks can make it worse.
Also look at "Carbs, Jetting, & Exhaust" (5th post down)
in the Table of Contents, Technical Documents/References