Older threads on this forum have said that the P19 has threaded backup plates, so I'm going on that assumption. The 6 other bolts came out cleanly, and then snugged up tight when I ran them back in. The heads of the last 2 came off almost immediately when trying to back them out, so I'm thinking either they were torqued down way too tight by the previous owner, or they have seized on the aluminum, due to no grease being applied to the threads (hopefully the former). You're right that nuts on the backside would make removal of the bolts easier, but there's a bulkhead in the way between the inspection port and the transom, and I'd like to avoid cutting through that, if at all possible.