Another thought I had was a piece of flat steel bar, 50mm wide or a little wider.
Cut a hole in it at one end for the socket to go through with two smaller holes either side of that to bolt it to the crank pulley.
Some 8mm threaded rod inserted in to the pulley holes and a series of nuts down the length of it to secure it and add some strength. The other end of the thread rods through the bar and a couple more nuts to secure it all together.
Make it long enough to brace against the chassis rail. Might need to strengthen the handle to stop it flexing under load - possibly with some bits of wood on each side and bolted through the bar, a bit like the handle on a kitchen knife.
Clive, could you let me know how far apart two opposing holes are from your tool?
Am I right in thinking the bolt takes a 24mm socket?
Edit: just picked up 2 metres of 50mm x 25mm box section from work for free. Should do nicely and not need the wooden braces!
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