360 to replace 273

In addition to above, If you are going to use your original transmission, you'll need a bushing to go over the outside of the older smaller torque converter pilot, and fit the larger, newer 360 crank register

If you use the old style water pump, which puts the lower output on the correct side for your existing radiator, the timing marks won't be useable, and I'm not sure whether/ not you can mix the new balancer with the old timing cover. You do NOT want to use the old balancer on the 360. What this means is, if you can use the proper/ new balancer with the old timing cover, you'll have to use a piston stop and remark the balancer.

THIS IS NOT a big deal, I can step you through that.

If the new balancer will not work with the old timing cover, you'll have to use all new style timing cover/ water pump, which then puts the pump outlet on the wrong side. So you'll need either a new radiator, or to have the lower outlet swapped side--to side.

I "cheated" on mine. I'm using all--new style water pump/ timing cover, but the old radiator. I have two hoses of unknown origin, which runs under the balancer in the front corner of the K member to "get to the other side."