I shudder (and certainly the Anson's airframe shuddered) at the thought. Only possible scenario involves substantial "downhill" entry to build up airspeed prior to the attempt, then a straining, groaning climb toward an apex where (a) airspeed would have certainly dropped to near zero, raising likelihood of simply falling from the sky inverted, and (b) much unsecured gear and a variety of unnecessary parts and components would have littered the overhead. Then there was recovery, probably easier, but no less thrilling. In retrospect, an Immelman might have been a equally colorful yet less perilous alternative. I suspect that the Anson's airframe was strong enough to keep the wingspars conjoined, and your Dad was flying in an era in which aviators, in their own eyes avatars, routinely attempted maneuvers which designers had not intended a/c to undertake. Many were successful, but then, the exposure risk to other perils was pretty high.

Let us never forget the acts, deeds and sacrifice of the men (and even some women) who flew then. When I think of aviators, I always recall an older cousin, a petite greying blond, barely 100 lbs, who ferried C-47s to the Scuppered Aisles. Long after the war, she used to claim that a combination of ineffective cockpit heat and sitting on a packed parachute to see ahead aggravated her arthritis which sadly limited her getting around late in life. They offered to let her go home after her brother was lost piloting a B-17 over Germany. Apparently, she claimed to keeping on keeping on was the preferred alternative.