Lee
You might drop a high temperature O ring probably a # 60 under the primer and see how the bolt closes with the O ring under the primer.
I am pretty sure that would solve the problem and I even have the proper 'o' ring for it but!!! the 'o' ring is not the long term answer and I am not sure it is the best answer.
I wish I had the abilty to build metal parts - if I could I would stick the plug in a lathe and turn the existing primer bench out of there, then contruct and install a new bench to the correct height - but i would also want it to be universal enough that you were not limited to just one length primer. I think I am darn close to that in my Remington conversion...
I might just take a plug out to Machine Shop Dave and see what he thinks it might take...