Seems to me if memory serves the one my buddy had would fit into the mounts another friend made in the school machine shop for our Big Jon electrics many moons ago. Your best bet might be to measure the base plates and have someone make you a set?
Not realizing that Luhr Jensen stopped making them, I left them at the lake where they've been in storage. I see there are some Scotty L brackets, I'm hoping I can adapt those to do the job.
Just an FYI for anyone finding some of the old Luhr Jensen downriggers at garbage sales etc. The standard Scotty downrigger mounting plates are about 1/8"-1/4" too narrow. You will need to shave off a bit off of the sides to get them to slide into the mount. You will also need some sort of shim to tighten the vertical gap in the mount since the LJ's have a thinner plate.