Metricnut -
Hopefully you followed the "swap made in heaven" directions from Patricks and exchanged the mounting plate with the original. My 216 had square holes (is this an oxymoron?) in the bottom of the plate while the newer '57 plate had no holes at all.
I suspect that the carrage bolts where just another securing safety to help prevent the nuts from vibrating off, or if they did to hopefully help hold the bolts in place until you discovered the missing nuts.
You may have already realized that the starboard side bolt must be installed prior to installing the front mounting bracket.
I just took a look in my Master Parts List and it only lists the bracket and bolts as one assembly.
Good luck
