The first fabricated tool I ever saw was using old head bolts with the heads cut off and a slot cut in the top as guides to get the engine head back on straight.
I like to make three of them, and put them on the last three bolts in the tightening pattern. Then when I install the rest of the bolts, I can remove them with a large slotted screwdriver and install the remaining three bolts, in sequence.
I like to use 2x6 with regular door hinges to build impromptu sheet metal brake of the size required. Also, threaded rod makes excellent clamps.
My dad could out-cobble anyone, though. He once took the front end of an old Ford truck and welded plates onto the stub axles and used cables and turnbuckles to mount a set of wheels to a small building in order to pull it down the road behind a tractor.