From my experience, if the crankshaft hub on the 360 is smaller then the hub on the converter, you are pretty screwed. A modern converter didn't fit in the trans, and the difference between the two hubs kept the flex plate too far away from the converter. That was years ago, things may be different now, but back then it couldn't be done with out changing the pump on the trans so the modern converter that fit into the crankshaft hub could be used.
You have it backwards, the hub on the early torque converter is smaller than the ring on the later crankshaft. Wildcat Auto sells, or used to, an annular ring to address that. I bought one a couple years ago to stuff an 87 318 into my 65 Cuda.
As for the engine mounting bracket, the ears on the 273 are wider than the 340/30 ears, on the driver's side. A couple of washers for a spacer fixes that. HOWEVER, there is a missing ear on the later blocks that the 273 bracket uses, you need that ear. Or you can buy a set of Schumacher mounts to address that, if they are being made anymore. I got a set out of Canada a couple years ago and it was hard to find.
