Ted,
Are you sure you have the correct spacer? I have a 51 216 with the Roch B. when the insulator (spacer) and the carb are installed there is not a whole lot of room for the hold down nuts for the carb. When I was doing my truck, and came across something like this, I had to ask myself which would be easier to change by a previous owner, the studs or the insulator. If the studs look like they have been there a long time, I would check that your insulator is correct.
Hope this helps. Let us know what you find.
Mark
