The plates bolt to the block, then your clamshells bolt to the adapter plates. I used the carshop inc setback plates and everything lined up great. dont use the transdapt plates as they are not meant for clamshells. If you look at the carshop plates the clamshell mounting holes are moved down about 1/4" compared to most other mounts to make up for the added width of the plates and it makes the mounts line up real nice.