You are correct, two different sizes. You will need extra deep sockets and there is a set available for loan from this site. Do a search on keel bolts for more information about the Bolts and go to tools for information on borrowing the community set. If you want to buy your own, these can be found at Summit Racing however they are extra thick for impact use and might be a bit tight for the one bolt furthest aft on a C36MKll
John Meyer