I suspect the length of the keel bolts had something to do with the original ease of
installation. You could cut them off but its always best to chase down the thread with a die and then use the die to clean the threads coming off rather than trying to start onto a thread damaged by the cutting. Think in terms of leaving them long if you are contemplating
removal of the keel, however.
If these things are not real big (read 1.5 inch nuts or more) I would buy a crow foot wrench in half inch drive. Bigger sizes are available but you may not have enough torque with half inch drive on really big stock. I don’t think there is much out there for ¾ drive crowfoot wrenches. Get the one that looks like a cut-off open end. The ones for flare nuts are not nearly as strong.
The cutting and welding of a socket is a good idea, done correctly it is strong enough and would allow you to use a ¾ drive handle to break them loose and Find the correct size socket in a six point deep well. Make sure it is marked Chrome Vanadium as are most impact sockets. Find a piece of pipe (preferably sched 80 that has a slightly smaller I.D. than the sockets O.D.) cut the drive part of the socket off of the end. Machine the inside of the pipe, outside of the socket, or both to a press fit with the socket
parts. Press the
parts together nearly flush, makes the wall a lot thicker and makes it a lot less apt to break.
Weld a bead around both joints. Chrome Vanadium welds easily. Chrome plated sockets can be problematic. No need for stainless pipe, just makes it tougher to weld and hard to find in sched 80.
I make specialty tools like this all the time and used them with impact wrenches on occasion.