Neil, an interesting event! One of the few breakages that is failsafe in an engine. I have seen chafed alloy pushrods caused by using too large a washer under the short head bolt between the two cylinders, most commonly on A65s where alloy pushrods are standard. There is very little clearance here on both A10s and A65s.
Regarding alloy versus steel pushrods, there is a lot we can learn from the American high-performance V8 community, Which really has bottomed out this issue. Alloy pushrods can be a good bet if they are short, and if the spring loads are not colossal, creating a situation where whip is not an issue. The aluminium alloys have a much lower Young's modulus than steel, so pushrods of any length are in variably made of steel tube. American spec 4130 tube is a popular choice, and for anyone interested, small quantities of small diameter 4130 tube can be bought from the companies that supply components for home built light aircraft. Titanium is generally not thought of as a good choice either, because it's Young's modulus is similar to that of the aluminium alloys.
HTH, Jon