Finding 360 engine/tranny to replace slant six

Good score on the 360 727 combo.
Vans would have the 727 stock.
Rebuild the trans you have, they are not that hard.
Bring a 1 1/4" socket, with extensions and rachet and see if the motor will turn over by hand, if so chances are it is a good canadate for rebuild.
Look at all the soft plugs, if none are compromised the block should not be cracked.