Was there a reliability and/or strength problem with the alloy rods? If you have a car with them, should you scrap them? What replacements, if any, are available?
There are several variations from 1936 - 1949. They basically get chunkier as time goes on but none should be trusted. If you are running with alloy rods then always change down and never labour your engine and stay below 3000 rpm.
There is some commonality between 3½ litre and XK so XK can be a source. With the 2½ litre you could possibly use 1½ litre rods but they require modification and you still need to make a balanced set of six.
Davenport Cars can supply 2½ litre modern steel rods. https://davenportcars.co.uk
Yes, frankly I would never trust alloy rods. All the. Post was rods will interchange on 3 1/2 engines except XJ 6.
For 2 1/2 engines we have always substituted a 3 1/2 litre crankshaft and used steel rods. So both getting rid of the alloy rods and gaining almost half a litre capacity and more torque.
And new modern design 3 1/2 cranks are made in Australia.