I just finished the same project on my 184 last fall. Crank broke just behind the #4 journal.
Might want to check out what I found as a root cause.http://www.farmallcub.com/phpBB2/viewtopic.php?f=31&t=65141&hilit=crankshaft
HamiltonBobsCubs has the best prices (and service) on crankshafts for the 154/184. I would purchase a crank from a 154 or 184 rather than the farmall cub. They might be the same, but why gamble if cranks are available.
If the driveshaft splines are worn then you will also need to replace the clutch. Driveshafts are available from a dealer, but only for a 184 without a creeper. If you have a creeper then you have to buy the longer driveshaft from the dealer and then have it shortened and turned down to fit. Take your original driveshaft to the machine shop so they can use it as a template.
Buy your clutch plate from HamiltonBobsCubs because the price at the dealer just increased significantly.