I've never heard of any serious problems among the conversion crowd. I see the potential for problems in the unusual location of the mounting point, and the semi-firm frame mounts. I can imagine that some serious torque could snap it off the t-case, but that would have to be a really huge engine, and a havy foot. Talking about the kind of power that makes people replace diffs and birfs after a liesurly commute.
The way the idiot PO of my 40 did his conversion, he mounted the t-case onto the prop-style crossmember with flexible rubber mounts, but bolted the engine directly onto the stock F frame mounts with a jerry-rigged bracket. Flexible mounts and solid mounts on either end of a driveline are a recipe for unpleasantness. Then again, the PO in question did put a fawking chebby V8 in there, so I know he's whimsical in the brainpain...
* for you pro-V8 conversion guys out there, the last comment was intended for levity. No I don't think Chevota people are insane, how you mutilate your cruiser is between you and your cruiser.