Thanks for the replies Norm and Max,
My heat gun stopped working about 12 months ago and I am a bit lost without it. Guess I got a bit frustrated with those bearings, but they were unbelievably tight. I showed the rim to a welder and he thinks the cracks are repairable, but would take someone very skilled with welding cast material. He actually suggested against it and said to burr out the cracks with a dremel and maybe drill a few small holes into the cracks in a couple places, then fill with a strong metal epoxy like JB Weld. Then sand back to original. He thinks that would probably be as strong as the original casting, which might have had a flaw in it from the time it left the foundry.
I will look into your idea Norm, but most of the new wheels I've looked at have the bearing a bit proud of the hub, so there is nothing to cut out. I've done a lot of searching but so far the only wheels that come close are solid cushion rubber with minimal tread (280mm diameter with a 54mm hub width), and an inflatable one measuring 260mm with a 54mm hub length. But that last one would have to come from the US, so too expensive to consider.
Failing all that, get another one cast, which could be the most expensive option.
A friend told me about a HD25 he saw advertised locally but did not tell me about it, so I missed out. Haven't seen a Rover Colt for probably 15 years.
