They are common on old cars/trucks. I have several. Model A Fords have a number of them. The motors have several, and a wrench will not work as the area around the bolt/not is confined, so only a socket will fit there.
My hobby is cars from the late 20's/early 30's so all of my wrenching is SAE. I purchased my first Craftsman tool set in 1965. Still using it... but have added flea market finds of Craftsman stuff.
I work on older cars and trucks frequently. Square bolts and nuts are in use there quite a bit The 8-point sockets are nicer to use than an open end wrench of loosening/tightening nuts and bolts.
Just rent a Cement cutting circular saw and cut down your distance. If you need it wider, you will need to remove the metal surrounds on the exiting window. we did this when we added our den to the side of our existing house 20+ years ago.
They are definitely router bits. Not nearly as well made or machined as present day bits. More than 40 years ago I bought a set of about 10-12 of them from a mail order company that I believe was in California, Harbor Freight!
I would not attach them to the horizontal planks unless the planks were bolted completely through. Otherwise it is just false security that they are actually helping to hold up the racks.
I recently picked up the Masterforce long reach jack from Menards. I really like it and would believe it to be comparable to the HF ones. Price was something in the $230.00 range.
All this concern about the solids dropping out and being left behind.... remember that periodically during each day, sink water or tub/shower water will be washing down the drain, taking anything left behind.
Acetone is a frequent solvent in most chemistry labs. We kept the in-use acetone in a squeeze bottle with a small hole in the top. Otherwise, acetone will weep out the spout on its own. You just place your finger over the small hole (Perhaps 1/8" diameter) when you want to squeeze some out...
Pour some sea foam directly into the cylinder (Remove spark plug), let it sit for 15 minutes or so, then start up the motor. It will smoke quite a bit, but it will clean the carbon off of the piston head. We do this on our model A Ford's when necessary.