"as the front pulley will turn while the flywheel will not."
Indicative, but not definitive. Does the retaining nut rotate? I try not to assume any more than absolutely necessary.
I have experienced a broken crank (Landrover, not a tractor). It was down to either wrong radius at journal-to-web, improper surface hardening or just turned too small (I thought the first option was most likely at the time). Engine ran for some time with the crank broken and no problem -just replaced the crank. But you will not know until you check it out. Possibility the block needs line-boring, too.